case study questions in java

Review these 50 questions to crack your Java programming interview

by javinpaul

A list of frequently asked Java questions from programming job interviews.

Hello, everybody! Over the past few years, I have been sharing a lot of Java Interview questions and discussion individually. Many of my readers have requested that I bring them together so that they can have them in the same spot. This post is the result of that.

This article contains more than 50 Java Interview questions covering all important topics like Core Java fundamentals, Java Collection Framework , Java Multithreading and Concurrency , Java IO , JDBC , JVM Internals , Coding Problems , Object-Oriented programming , etc.

The questions are also picked up from various interviews and they are, by no means, very difficult. You might have seen them already in your phone or face-to-face round of interviews.

The questions are also very useful to review important topics like multithreading and collections. I have also shared some useful resources for further learning and improvement like The Complete Java MasterClass to brush up and fill gaps in your Java skills.

So what are we waiting for? Here is the list of some of the most frequently asked Java questions in interviews for both beginner and experienced Java developers.

50+ Java Interview Questions for 2 to 3 years Experienced Programmers

So, without wasting any more of your time, here is my list of some of the frequently asked Core Java Interview Question s for beginner programmers. This list focuses on beginners and less experienced devs, like someone with 2 to 3 years of experience in Java.

1) How does Java achieve platform independence? ( answer ) hint: bytecode and Java Virtual Machine

2) What is ClassLoader in Java? ( answer ) hint: part of JVM that loads bytecodes for classes. You can write your own.

3) Write a Java program to check if a number is Even or Odd? ( answer ) hint: you can use bitwise operator, like bitwise AND, remember, even the number has zero at the end in binary format and an odd number has 1 in the end.

4) Difference between ArrayList and HashSet in Java? ( answer ) hint: all differences between List and Set are applicable here, e.g. ordering, duplicates, random search, etc. See Java Fundamentals: Collections by Richard Warburton to learn more about ArrayList, HashSet and other important Collections in Java.

5) What is double checked locking in Singleton? ( answer ) hint: two-time check whether instances is initialized or not, first without locking and second with locking.

6) How do you create thread-safe Singleton in Java? ( answer ) hint: many ways, like using Enum or by using double-checked locking pattern or using a nested static class.

7) When to use the volatile variable in Java? ( answer ) hint: when you need to instruct the JVM that a variable can be modified by multiple threads and give hint to JVM that does not cache its value.

8) When to use a transient variable in Java? ( answer ) hint: when you want to make a variable non-serializable in a class, which implements the Serializable interface. In other words, you can use it for a variable whose value you don’t want to save. See The Complete Java MasterClass to learn about transient variables in Java.

9) Difference between the transient and volatile variable in Java? ( answer ) hint: totally different, one used in the context of serialization while the other is used in concurrency.

10) Difference between Serializable and Externalizable in Java? ( answer ) hint: Externalizable gives you more control over the Serialization process.

11) Can we override the private method in Java? ( answer ) hint: No, because it’s not visible in the subclass, a primary requirement for overriding a method in Java.

12) Difference between Hashtable and HashMap in Java? ( answer ) hint: several but most important is Hashtable , which is synchronized, while HashMap is not. It's also legacy and slow as compared to HashMap .

13) Difference between List and Set in Java? ( answer ) hint: List is ordered and allows duplicate. Set is unordered and doesn't allow duplicate elements.

14) Difference between ArrayList and Vector in Java ( answer ) hint: Many, but most important is that ArrayList is non-synchronized and fast while Vector is synchronized and slow. It's also legacy class like Hashtable .

15) Difference between Hashtable and ConcurrentHashMap in Java? ( answer ) hint: more scalable. See Java Fundamentals: Collections by Richard Warburton to learn more.

16) How does ConcurrentHashMap achieve scalability? ( answer ) hint: by dividing the map into segments and only locking during the write operation.

17) Which two methods you will override for an Object to be used as Key in HashMap ? ( answer ) hint: equals and hashcode

18) Difference between wait and sleep in Java? ( answer ) hint: The wait() method releases the lock or monitor, while sleep doesn't.

19) Difference between notify and notifyAll in Java? ( answer ) hint: notify notifies one random thread is waiting for that lock while notifyAll inform to all threads waiting for a monitor. If you are certain that only one thread is waiting then use notify , or else notifyAll is better. See Threading Essentials Mini-Course by Java Champion Heinz Kabutz to learn more about threading basics.

20) Why you override hashcode, along with equals() in Java? ( answer ) hint: to be compliant with equals and hashcode contract, which is required if you are planning to store your object into collection classes, e.g. HashMap or ArrayList .

21) What is the load factor of HashMap means? ( answer ) hint: The threshold that triggers the re-sizing of HashMap is generally 0.75, which means HashMap resize itself if it's 75 percent full.

22) Difference between ArrayList and LinkedList in Java? ( answer ) hint: same as an array and linked list, one allows random search while other doesn't. Insertion and deletion easy on the linked list but a search is easy on an array. See Java Fundamentals: Collections , Richard Warburton’s course on Pluralsight, to learn more about essential Collection data structure in Java.

23) Difference between CountDownLatch and CyclicBarrier in Java? ( answer ) hint: You can reuse CyclicBarrier after the barrier is broken but you cannot reuse CountDownLatch after the count reaches to zero.

24) When do you use Runnable vs Thread in Java? ( answer ) hint: always

25) What is the meaning of Enum being type-safe in Java? ( answer ) hint: It means you cannot assign an instance of different Enum type to an Enum variable. e.g. if you have a variable like DayOfWeek day then you cannot assign it value from DayOfMonth enum.

26) How does Autoboxing of Integer work in Java? ( answer ) hint: By using the valueOf() method in Java.

27) Difference between PATH and Classpath in Java? ( answer ) hint: PATH is used by the operating system while Classpath is used by JVM to locate Java binary, e.g. JAR files or Class files. See Java Fundamentals: The Core Platform to learn more about PATH , Classpath , and other Java environment variable.

28) Difference between method overloading and overriding in Java? ( answer ) hint: Overriding happens at subclass while overloading happens in the same class. Also, overriding is a runtime activity while overloading is resolved at compile time.

29) How do you prevent a class from being sub-classed in Java? ( answer ) hint: just make its constructor private

30) How do you restrict your class from being used by your client? ( answer ) hint: make the constructor private or throw an exception from the constructor

31) Difference between StringBuilder and StringBuffer in Java? ( answer ) hint: StringBuilder is not synchronized while StringBuffer is synchronized.

32) Difference between Polymorphism and Inheritance in Java? ( answer ) hint: Inheritance allows code reuse and builds the relationship between class, which is required by Polymorphism, which provides dynamic behavior. See Java Fundamentals: Object-Oriented Design to learn more about OOP features.

33) Can we override static method in Java? ( answer ) hint: No, because overriding resolves at runtime while static method call is resolved at compile time.

34) Can we access the private method in Java? ( answer ) hint: yes, in the same class but not outside the class

35) Difference between interface and abstract class in Java? ( answer ) hint: from Java 8 , the difference is blurred. However, a Java class can still implement multiple interfaces but can only extend one class.

36) Difference between DOM and SAX parser in Java? ( answer ) hint: DOM loads whole XML File in memory while SAX doesn’t. It is an event-based parser and can be used to parse a large file, but DOM is fast and should be preferred for small files.

37) Difference between throw and throws keyword in Java? ( answer ) hint: throws declare what exception a method can throw in case of error but throw keyword actually throws an exception. See Java Fundamentals: Exception Handling to learn more about Exception handling in Java.

38) Difference between fail-safe and fail-fast iterators in Java? ( answer ) hint: fail-safe doesn’t throw ConcurrentModificationException while fail-fast does whenever they detect an outside change on the underlying collection while iterating over it.

39) Difference between Iterator and Enumeration in Java? ( answer ) hint: Iterator also gives you the ability to remove an element while iterating while Enumeration doesn’t allow that.

40) What is IdentityHashMap in Java? ( answer ) hint: A Map , which uses the == equality operator to check equality instead of the equals() method.

41) What is the String pool in Java? ( answer ) hint: A pool of String literals. Remember it's moved to heap from perm gen space in JDK 7.

42) Can a Serializable class contains a non-serializable field in Java? ( answer ) hint: Yes, but you need to make it either static or transient.

43) Difference between this and super in Java? ( answer ) hint: this refers to the current instance while super refers to an instance of the superclass.

44) Difference between Comparator and Comparable in Java? ( answer ) hint: Comparator defines custom ordering while Comparable defines the natural order of objects, e.g. the alphabetic order for String . See The Complete Java MasterClass to learn more about sorting in Java.

45) Difference between java.util.Date and java.sql.Date in Java? ( answer ) hint: former contains both date and time while later contains only date part.

46) Why wait and notify method are declared in Object class in Java? ( answer ) hint: because they require lock which is only available to an object.

47) Why Java doesn’t support multiple inheritances? ( answer ) hint: It doesn’t support because of a bad experience with C++, but with Java 8, it does in some sense — only multiple inheritances of Type are not supported in Java now.

48) Difference between checked and unchecked Exception in Java? ( answer ) hint: In case of checked, you must handle exception using catch block, while in case of unchecked, it’s up to you; compile will not bother you.

49) Difference between Error and Exception in Java? ( answer ) hint: I am tired of typing please check the answer

50) Difference between Race condition and Deadlock in Java? ( answer ) hint: both are errors that occur in a concurrent application, one occurs because of thread scheduling while others occur because of poor coding. See Multithreading and Parallel Computing in Java to learn more about deadlock, Race Conditions, and other multithreading issues.

Closing Notes

Thanks, You made it to the end of the article … Good luck with your programming interview! It’s certainly not going to be easy, but by following this roadmap and guide, you are one step closer to becoming a DevOps engineer .

If you like this article, then please share with your friends and colleagues, and don’t forget to follow javinpaul on Twitter!

Additional Resources

Java Interview Guide: 200+ Interview Questions and Answers
Spring Framework Interview Guide — 200+ Questions & Answers
Preparing For a Job Interview By John Sonmez
Java Programming Interview Exposed by Markham
Cracking the Coding Interview — 189 Questions and Answers
Data Structure and Algorithms Analysis for Job Interviews
130+ Java Interview Questions of Last 5 Years

P.S. — If you need some FREE resources to learn Java, you can check out this list of free Java courses to start your preparation. P. S. S. — I have not provided the answer to the interview questions shared in the image “ How many String objects are created in the code?” can you guess and explain?

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18 Java scenarios based interview Q&As for the experienced – Part 1

Let’s look at scenarios or problem statements & how would you go about handling those scenarios in Java. These scenarios interview questions will judge your Java experience. Full list of Java scenarios based interview questions are covered at Judging your Java experience via scenarios based interview Q&As .

#1. Caching

Q01.Scenario : You need to load stock exchange security codes with price from a database and cache them for performance. The security codes need to be refreshed say every 30 minutes. This cached data needs to be populated and refreshed by a single writer thread and read by several reader threads. How will you ensure that your read/write solution is scalable and thread safe?

Cache for read performance

A01. Solution : There are a number of options as described below:

Option 1 : The java.util.concurrent.locks package provides classes that implement read/write locks where the read lock can be executed in parallel by multiple threads and the write lock can be held by only a single thread. The ReadWriteLock interface maintains a pair of associated locks, one for read-only and one for writing. The readLock( ) may be held simultaneously by multiple reader threads, while the writeLock( ) is exclusive. In general, this implementation improves performance and scalability when compared to the mutex locks (i.e. via synchronized key word) when

1. There are more reads and read duration compared to writes and write duration .

2. It also depends on the machine you are running on — for example, multi-core processors for better parallelism .

Here is another approach step by step: Simple caching Java application step by step

Option 2 : The ConcurrentHashmap is another example where improved performance can be achieved when you have more reads than writes . The ConcurrentHashmap allows concurrent reads and locks only the buckets that are used for modification or insertion of data.

Option 3 : Making use of caching frameworks like EHCache , OSCache , etc. Caching frameworks take care of better memory management with LRU (Least Recently Used) and FIFO(First In First Out) eviction strategies, disk overflow, data expiration and many other optional advanced features, as opposed to writing your own.

Here is a working example in Java to Implement an in-memory LRU cache in Java with TTL without using a framework like EHCache.

Option 4 : Using a distributed & an in memory database like Redis . Redis can be a choice for implementing a highly available in-memory cache to decrease data access latency, increase throughput, and ease the load off your relational or NoSQL database and application.

#2. Asynchronus processing

Q02. Scenario : If you have a requirement to generate online reports or feed files by pulling out millions of historical records from a database, what questions will you ask, and how will you go about designing it?

A02. Designing a system is all about asking the right questions to gather requirements.

— Online Vs Offline? Should we restrict the online reports for only last 12 months of data to minimise the report size and to get better performance, and provide reports/feeds for the data older than 12 months via offline processing? For example, Bank statements for last 12 months via online & for transactions older than 12 months via offline asynchronous processing without blocking the customer from browsing rest of the website. Reports can be generated asynchronously and once ready can be emailed or downloaded via a URL at a later time.

— What report generation framework to use like Jasper Reports , Open CSV , XSL-FO with Apache FOP , etc depending on the required output formats?

— How to handle exceptional scenarios? send an error email, use a monitoring system like Tivoli or Nagios to raise production support tickets on failures, etc?

— Security requirements. Are we sending feed/report with PII (i.e. Personally Identifiable Information) data via email? Do we need proper access control to restrict who can generate which online reports? Should we password protect the email attachments? Are there any compliance or regulatory requirements like PCI (i.e. Payment Card Industry), GDPR (i.e. General Data Protection Regulation), ACCC (i.e. Australian Competition and Consumer Commission), etc depending on the jurisdictions served by the application?

— Should we schedule the offline reports to run during off peak time ? For example, enter all the requests for a report into a “ Request ” table and then schedule a process to run at say midnight to refer to all pending requests in the “ Request ” table to generate and store the relevant reports in an outbox for the customers to download. An email can be sent to clients with the report URL to download the report.

— Archival and purging straggles of the historical reports. What is the report retention period for the requirements relating to auditing and compliance purpose? How big are the files?

Solution : An online application with a requirement to produce time consuming reports or a business process (e.g. re-balancing accounts, aggregating hierarchical information, etc) could benefit from making these long running operations asynchronous. Once the reports or the long running business process is completed, the outcome can be communicated to the user via emails or asynchronously refreshing the web page via techniques known as “ server push (JEE Async Servlet)” or “ client pull (Refresh meta tag)”. A typical example would be

a) A user makes an online request for an aggregate report or a business process like re-balancing his/her portfolios.

b) The user request will be saved to a database table for a separate process to periodically pick it up and process it asynchronously.

c) The user could now continue to perform other functionality of the website without being blocked .

d) A separate process running on the same machine or different machine can periodically scan the table for any entries and produce the necessary reports or execute the relevant business process. This could be a scheduled job that runs once during off-peak or every 10 minutes. This depends on the business requirement.

e) Once the report or the process is completed, notify the user via emails or making the report available online to be downloaded.

Offline report generation on AWS cloud

#3 Regular Expressions (i.e. regex)

Q03. Scenario : You need to find and change a text from “Client” to “Customer” in 300+ html files.

A03. Solution : Harness the power of Unix & Regex .

sed and awk are very powerful Unix commands for file manipulations. These are covered in detail in The Unix interview Q&As .

#4 Auditing

Q04. Scenario : You have a requirement to maintain a history of insertion, modification, and deletion to the “Customer” table. How will you go about accomplishing this?

A04. Solution

1) Create an ETL (i.e. Extract Transform & Load) batch job that periodically extracts all the changes to batch files and send those files to a Data warehouse system, which loads these batch files to a SCD Type 2 history table. SCD Type 2 means maintain each change. This is discussed in detail at 13 Data Warehouse interview Q&As – Fact Vs Dimension, CDC, SCD, etc .

2) Asynchronously via publish & subscription paradigm. Publish each change as an event to a message oriented middle-ware like Apache Kafka, Rabbit MQ, Websphere MQ, etc & separate subscriber application will save each event to a SQL or NoSQL history table.

3) Create database table triggers to insert superseded records to a separate history table. A database trigger is procedural code that is automatically executed in response to certain events like insert, update, etc on a particular table or view in a database. Care must be taken in using or writing triggers as incorrectly written or used triggers can significantly impact performance of your database.

#5 Externalize business rules

Q05. Scenario : You are asked to design an application, which validates data with 100+ rules to comply with the government compliance requirements and tax laws. These compliance requirements can change and the application need to quickly and easily adapt to changing requirements.

A05. Solution : Harness the power of Rules Engines like Drools . Drools is a popular open source business rules and work flow engine. It helps you externalise the rules in database tables or excel spreadsheets as opposed to embedding within the Java code. The rules are executed in the form of when given a ($condition) then execute the ($consequence). The business will be the custodian of these rules that can be easily viewed on an excel spreadsheet or via querying the database tables. A GUI could be built to maintain these rules that reside in a database.

#6 Concurrency Management

Q06. Scenario : Reference counting where a shared resource is incremented or decremented. The increment/decrement operations must be thread safe. For example, a counter that keeps track of the number of active logged in users by incrementing the count when users log in and decrementing the count when the users log out. Sometimes you want to allow a finite number of concurrent accesses say 3 users at a time.

A06. Solution :

Mutex : is a single key to an object (E.g. a toilet). One person can have the key and occupy the toilet at the time. When finished, the person gives (or releases) the key to the next person in the queue. In Java, every object has a mutex and only a single thread can get hold of a mutex .

Semaphore : Is a number of free identical toilet keys. For example, having 3 toilets with identical locks and keys. The semaphore count is set to 3 at beginning and then the count is decremented as people are acquiring the key to the toilets. If all toilets are full, i.e. there are no free keys left, the semaphore count is 0. Now, when one person leaves the toilet, semaphore is increased to 1 (one free key), and given to the next person in the queue.

#7 Designing a trading system

Q07. Scenario : If you are working with an online trading application, you may want the functionality to queue trades placed after hours and process them when the stock market opens. You also need to asynchronously handle the order statuses sent from the stock exchange like partially-filled, rejected, fully filled, etc, and update the online order information. How will you go about solution this?

A07. Solution : The Message Oriented Middle-wares like Apache Kafka, Rabbit MQ, Websphere MQ, webMethods Broker, etc provide features like guaranteed delivery with store-and-forward mechanism, no duplicates, and transaction management for enterprise level program-to-program communications by sending and receiving messages asynchronously (or synchronously). The diagram below gives a big picture.

When using Message Oriented Middle-wares (MOM) to facilitate asynchronous processing

1) The producer (i.e Trading Engine) that submits user requests and consumer (i.e. FIX Router) that converts the messages to FIX protocol and send FIX messages to the Stock Exchange system retain processing control and do not block. In other words, they continue processing regardless of the state of others. Queue depths need to be properly set, and the messages need to be durable . Message correlation ids are used to pair request and response.

2) MOM creates looser coupling among systems, provides delivery guarantees, prevents message losses, scales well by decoupling performance characteristics of each system, has high availability and does not require same time availability of all sub-systems. So, MOM is ideal for geographically dispersed systems requiring flexibility, scalability, and reliability.

3) You may also require to perform logging, auditing and performance metrics gathering asynchronously and non-intrusively. For example, you could send the log messages from log4j to a queue to be processed later asynchronously by a separate process running on the same machine or a separate machine. The performance metrics can be processed asynchronously as well.

For example, a trading application may have a number of synchronous and asynchronous moving parts and metrics needs to be recorded for various operations like placing a trade on to a queue, receiving asynchronous responses from the stock market, correlating order ids, linking similar order ids, etc. A custom metrics gathering solution can be accomplished by logging the relevant metrics to a database and then running relevant aggregate queries or writing to a file system and then running PERL based text searches to aggregate the results to a “csv” based file to be opened and analyzed in a spreadsheet with graphs. In my view, writing to a database provides a greater flexibility. For example, in Java, the following approach can be used.

Asynchronous logging

— Use log4j JMS appender or a custom JMS appender to send log messages to a queue.

— Use this appender in your application via Aspect Oriented Programming (AOP – e.g Spring AOP, AspectJ, etc) or dynamic proxy classes to non-intrusively log relevant metrics to a queue. It is worth looking at Perf4j and context based logging with MDC (Mapped Diagnostic Contexts) or NDC (Nested Diagnostic Contexts) to log on a per thread basis to correlate or link relevant operations.

— A stand-alone listener application needs to be developed to dequeue the performance metrics messages from the queue and write to a database or a file system for further analysis and reporting purpose. This listener could be written in Java as a JMX service using JMS or via broker service like webMethods, TIBCO, etc.

— Finally, relevant SQL or regular expression based queries can be written to aggregate and report relevant metrics in a customized way.

#8 Impact Analysis (aka IA)

Q08. Scenario : You are required to change the logic of a module that many other modules have dependency on. How would you go about making the changes without impacting dependent systems.

A08. Solution : You need to firstly perform an impact analysis . Impact analysis is about being able to tell which pieces of code, packages, modules, and projects use given piece of code, packages, modules, and projects, or vice versa is a very difficult thing.

Performing an impact analysis is not a trivial task, and there is not a single tool that can cater for every scenario. You can make use of some static analysis tools like IDEs (e.g. eclipse), JRipples , X- Ray , etc. But, unfortunately applying just static analysis alone not enough, especially in Java and other modern languages whereas lots of things can happen in run time via reflections, dynamic class loading & configuration, polymorphism, byte code injection, proxies, etc.

a) In eclipse Ctrl+Shift+g c an be used to search for references

b) You can perform a general “File Search” for keywords on all projects in the work-space.

c) You can use Notepad++ editor and select Search –> Find in files. You can search for a URL or any keyword across a number of files within a folder.

There are instances where you need to perform impact analysis across stored procedures, various services, URLs, environment properties, batch processes, etc. This will require a wider analysis across projects and repositories.

Search within your code repository like GIT :

Tools like FishEye can be used to search across various code repositories. FisheEye is not targeted for any special programming language. It just supports various version control systems and the concept of text files being changed over time by various people. Handy for text searches like environment based properties files to change a URL or host name from A to B.

Grep the Unix/Linux environment where your application is deployed.You can perform a search on the file system where your application(s) are deployed.

Analyze across various log files . It is also not easy to monitor service oriented architectures. You can use tools like Splunk to trace transactions across the IT stack while being tested by the testers to proactively identify any issues related to change. Splunk goes across multiple log files.

Conduct impact analysis sessions across cross functional and system teams and communicate the changes . Brain storm major areas affected and document them. Have a manual test plan that covers the impact systems to be tested. Collaborate with cross functional teams and identify any gaps in your analysis. Have a proper review and sign-off process. Get more developers to do peer code reviews.

Have proper documentation with high level architecture diagrams and dependency graphs where possible . As the number systems grow, so does the complexity. A typical enterprise Java application makes use of different database servers, messaging servers, ERP systems, BPM systems, Work flow systems, SOA architectures, etc. Use online document management systems like Confluence or Wiki , which enables search for various documents.

More Java scenarios based interview Q&As

Q09 to Q18: 18 Java scenarios based interview Q&As for the experienced – Part 2

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50 Java Interview Questions + 30 Scenario Based Q&A

This is post 2 of 8 in the series “Programming Language Interview Questions”

Object Oriented Programming (OOPs) Interview Questions
Cracking the Code: 200 Interview Q&A for Software Developers
Performance and Optimization Interview Questions
Caching Interview Questions and Answers
Error Handling and Debugging Interview Questions
C Programming Language Interview Questions
C++ Programming Interview Questions

Table of Contents

Introduction

Java is one of the most popular and widely used programming languages today. It is important for aspiring Java developers to be well-prepared for technical interviews which typically involve many Java programming questions.

The interviewers often ask a mix of theoretical Java questions to test the conceptual knowledge and practical programming questions to evaluate the coding skills. In this article, we provide a compilation of commonly asked Java interview questions and sample answers to help candidates prepare effectively.

The questions cover core Java basics, OOP concepts, classes and objects, methods and constructors, access modifiers, inheritance, polymorphism, abstraction, interfaces, Java collections, exception handling, multithreading and concurrency. There are also scenario-based Java questions that can be asked in interviews to check how candidates can apply the language features to build real-world applications.

50 interview questions and answers

1. What is Java? Java is a high-level, object-oriented programming language. It is a general-purpose concurrent and class-based language that is designed to have as few implementation dependencies as possible.

2. What are objects and classes in Java? Objects are basic building blocks in Java that contains state and behavior. Classes are templates that define objects and their behavior.

3. What is JVM and JRE? JVM (Java Virtual Machine) is the runtime environment for Java programs. It converts Java bytecode into machine language. JRE (Java Runtime Environment) is the implementation of JVM that provides core libraries and other components to run Java programs.

4. Explain the platform independence of Java. Java is compiled to bytecode that can run on any platform with a JVM. The JVM interprets the bytecode into native machine code. This makes Java platform independent.

5. What are constructors in Java? Constructors are special methods in Java that are used to initialize objects. The constructor is invoked when an object of a class is created. It has the same name as the class and does not have a return type.

6. What is method overloading and overriding in Java? Method overloading is defining methods with the same name but different parameters. Overriding is providing a specific implementation of a method already defined in the parent class.

7. What is abstraction in Java? Abstraction refers to hiding the implementation details and exposing only the functionality to users. Abstract classes and interfaces are used to achieve abstraction in Java.

8. What are Java packages? Packages in Java are collections of related classes and interfaces that are bundled together. Packages provide namespace management and access control in Java.

9. What is final keyword in Java? The final keyword is used to apply restrictions on classes, methods and variables. Final class cannot be inherited, final method cannot be overridden and final variable value cannot be changed.

10. What is static in Java? Static is a keyword in Java used to denote a class member belongs to a type rather than to an instance. Static members can be used without creating an object of class.

11. What is encapsulation in Java? Encapsulation is the mechanism of wrapping data (variables) and code acting on data (methods) together as a single unit. In Java, encapsulation is achieved by making fields private and providing public setter and getter methods.

12. What is inheritance in Java? Inheritance represents parent-child relationship between classes in Java. It allows a derived class to inherit commonly used state and behavior from its parent class.

13. What is polymorphism in Java? Polymorphism means ability to take different forms. In Java, polymorphism allows assigning a variable and method call to take different forms or classes. Method overloading and overriding uses polymorphism.

14. What is JIT compiler in Java? JIT (Just-In-Time) compiler in Java converts bytecode into native machine code at runtime when required by the program. It improves performance by compiling bytecode lazily.

15. What is multithreading in Java? Multithreading allows concurrent execution of multiple parts of a Java program. The main ways to create threads in Java are extending Thread class and implementing Runnable interface.

16. Explain different ways to create a thread in Java. There are two ways to create a thread in Java – 1. Extending Thread class 2. Implementing Runnable Interface. Runnable is preferred because Java does not support multiple inheritance.

17. What are access modifiers in Java? Java provides access control through public, protected, private and default modifiers. Public grants access from anywhere. Private restricts access to the class itself. Default and protected have specialized uses.

18. What is Collections Framework in Java? Java Collections Framework provides ready-made architecture to store and manipulate group of objects. It contains interfaces like List, Set, Queue and classes like ArrayList, LinkedHashSet, PriorityQueue etc.

19. What are different types of inner classes in Java? – Nested (static) inner class – Inner class – Local inner class – Anonymous inner class

They allow logical grouping of classes and interfaces and access to the outer class.

20. What is Java API and where is it documented? Java API (Application Programming Interface) is a collection of pre-built packages, classes and interfaces in Java. It is documented at https://docs.oracle.com/en/java/javase/index.html

21. What is JDBC API in Java? JDBC (Java Database Connectivity) is an API used to connect and execute queries to a database from Java. JDBC provides a set of interfaces that allows connectivity to relational databases.

22. What are the basic interfaces of JDBC API? The core interfaces of JDBC API are – Driver, Connection, Statement and ResultSet that allows connecting and interacting with a database.

23. What are the different types of JDBC drivers? There are 4 types of JDBC drivers: 1. JDBC-ODBC bridge driver 2. Native API driver (partially java driver) 3. Network Protocol driver (fully java driver) 4. Thin driver (fully java driver)

24. What is singleton class in Java and how can we make a class singleton? Singleton class means that only one instance of the class can be created. Singleton pattern involves a single private constructor, a static variable and a static public method that returns the instance.

25. What is Java Serialization API? Java Serialization API provides a standard mechanism to serialize objects to stored or transmitted across streams. Only serializable objects can be serialized.

26. How can we convert bytes to objects and vice-versa in Java? We can convert bytes to objects and vice-versa using serialization and deserialization in Java. ObjectOutputStream is used to convert objects to bytes and ObjectInputStream is used to recreate objects from bytes.

27. What are anonymous inner classes in Java? Anonymous inner classes are inner classes without a name declared and instantiated in a single expression using the new keyword. They are used for inline implementation of interfaces.

28. What is reflection API in Java and why is it useful? Java reflection API allows inspecting and modifying runtime behavior of classes at runtime. It is useful to introspect objects and call methods dynamically at runtime without knowing the names at compile time.

29. What is autoboxing and unboxing in Java? Autoboxing is automatic conversion of primitive types to object wrapper classes. Unboxing is the reverse process of converting wrapper objects to primitives. They were introduced in Java 1.5.

30. What is final, finally and finalize in Java? final is a keyword – final class can’t be inherited, final method can’t be overridden, final variable value can’t change. finally is a block – used with try/catch to put code that executes always. finalize is a method – called by Garbage collector before object is collected.

31. What is try-with-resources in Java? try-with-resources is a way to automatically close resources after usage without needing an explicit finally block. Any class that implements AutoCloseable interface can be used in try-with-resources.

32. What is multi-catch block in Java? A multi-catch block allows handling multiple exceptions in a single catch block instead of using multiple catch blocks for different exceptions. The catch parameter is specified using pipe (|) symbol.

33. What are the advantages of Java? Simple, Object-Oriented, Portable, Platform independent, Secured, Robust, Architecturally neutral, Interpreted, High Performance, Multithreaded, Distributed, Dynamic

34. What are the disadvantages of Java? Not suitable for low-level programming. Limited speed. No unsigned data type. Backward incompatible.

35. What is namespace in Java? Namespace is a naming system to organize classes in Java packages. It resolves naming collisions and confusions and allows fully qualified name to uniquely identify classes, interfaces etc.

36. What is JIT compiler in Java? JIT (Just-In-Time) compiler is used to improve the performance. It converts bytecode into native machine language when required by the running Java program.

37. What is the difference between path and classpath variables? PATH is an environment variable used by operating system to locate executables. Classpath is specific to Java and used by JVM to locate Java bytecode files (classes).

38. What is Anonymous inner class in Java? Anonymous inner class is an inner class without a name declared and instantiated in a single expression using the new operator. Commonly used for simplified event handling.

39. What is difference between Heap and Stack memory? Heap memory is used by all parts of the application whereas stack memory is used only by one thread of execution. Objects are created in Heap, Stack is used for local primitive variables and references to objects in Heap.

40. What is Java String Pool? Java String Pool refers to collection of Strings stored in heap memory. String literals and constants are stored in the String pool for reuse to optimize memory usage.

41. How is a string immutable in Java? In Java, string objects are immutable meaning their state cannot be changed once created. Whenever changes are made to a string, a new instance is created. This optimizes performance by reusing strings from pool.

42. What is ThreadPoolExecutor in Java? ThreadPoolExecutor is a thread pool implementation added from Java 5 that provides more configurable thread pools to execute tasks. It allows configuring pool size, rejection policies, thread factories etc.

43. What is Java Memory Model? It is a specification that describes the shared memory system defined by the Java programming language and virtual machine including visibility and atomicity guarantees on shared data.

44. What is memory leak in Java? Memory leak occurs when objects are no longer used by the application but Garbage Collector fails to recognize them as unused. This results in out of memory errors if too many objects are unreferenced.

45. What is shallow copy and deep copy in Java? Shallow copy is copying an object’s field references into another instance. Deep copy is making separate copy of all the objects in the original object graph.

46. What are transient and volatile keywords in Java? transient – skip field during serialization, volatile – field will not be cached and always read from main memory.

47. What is Executor Framework in Java? The Executor framework in Java provides an abstraction over management of threads. Executors can schedule asynchronous tasks and control concurrency transparently using thread pool.

48. Explain Generics in Java? Generics allow defining type-safe classes, interfaces and methods which work with different types while avoiding duplicity. Generics work only with reference types in Java.

49. What is Comparable and Comparator interface in Java? Comparable is used to provide natural ordering of objects of a class. Comparator provides custom ordering and added flexibility of sorting objects.

50. Explain different ways to iterate over a collection in Java? Iterating collections can be done through Iterator, for-each loop, forEach(), forEachRemaining() and ListIterator. Iterator allows removing elements during iteration while ListIterator can iterate in reverse.

30 scenarios based interview questions and answers

1. How will you find if a string contains only digits in Java? I can use matches() method of string to match the given string against a regular expression that matches digits like below:

String str = “123”; boolean result = str.matches(“[0-9]+”);

2. How can you swap two numbers without using a temporary variable in Java? We can use arithmetic operators to swap two numbers:

int a = 5; int b = 10;

a = a + b; b = a – b; a = a – b;

3. How can you reverse a string in Java without using any library method? We can write a for loop which starts from the end of the string and appends each character to form the reverse string.

StringBuilder reversed = new StringBuilder();

for(int i = str.length()-1; i >= 0 ; i–){ reversed.append(str.charAt(i)); }

4. How can you find duplicate elements in an array in Java? Iterate through array and store elements as key in a HashMap. If element is already present, print it as duplicate. Time complexity is O(n) and space is O(n).

5. How can you find the largest and smallest number in an unsorted integer array in Java? Iterate through array keeping track of min and max element so far. Time complexity is O(n) to traverse array once.

6. How can you remove duplicates from an array without using any library in Java? Add elements to HashSet which lets only unique elements. Then add set back to array. Time complexity is O(n).

7. How can you find the factorial of a number in Java? Factorial can be calculated using recursion. Base case is f(0) = f(1) = 1. General case is f(n) = n * f(n-1).

8. How can you check if two string are anagrams in Java? 1. Check if length is same 2. Convert strings to char array 3. Sort the char arrays 4. Check if both arrays are equal

9. How can you design a vending machine in Java? Vending machine would have attributes like currentQuantity, pricePerItem. Methods like insertMoney(), selectItem(), dispenseItem(), giveChange() which implement the vending logic.

10. How can you check if a string contains only alphabets in Java? Use matches() with regex “[a-zA-Z]+” to check if string has only alphabets.

11. How can you find whether a year is leap year or not in Java? If year is divisible by 4 and not 100, or divisible by 400, then it is a leap year.

if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0) System.out.println(“Leap year”); else System.out.println(“Not a leap year”);

12. How can you swap two Strings without using a temporary variable? We can use StringBuilder’s append() method to swap strings.

string1 = string1.concat(string2); string2 = string1.substring(0, string1.length()-string2.length()); string1 = string1.substring(string2.length());

13. How can you find the middle element of a linked list in Java? – Iterate through linked list to find total length – Traverse till length/2 to find middle element

14. How can you reverse a linked list iteratively and recursively?

1. Initialize prev, current and next 2. In loop, make next = current.next, current.next = prev, prev = current

1. Base case: head or head.next is null 2. Recursively call reverse() on head.next 3. Attach head to the end of reversed list

15. How can you find if a linked list contains a cycle in Java? Use two pointers – fast that moves 2 nodes ahead and slow that moves 1 node. If cycle exists, fast and slow will meet at some node.

16. How can you implement a stack using array and linked list?

Array: Use array, top pointer and push(), pop() operations. Linked List: Use linked list node with next pointer. top pointer and push(), pop() operations.

17. How can you implement a queue using array in Java? Use array, front and rear index, enqueue() and dequeue() operations. Handle queue full and empty conditions.

18. How can you find all permutations of a String in Java? Use recursion. For each char, fix it and find permutations of remaining chars. Add fixed char to beginning and append permutations.

19. How can you design a parking lot using OOPS in Java? ParkingLot class has attributes like totalSpots, availableSpots. Car class has regNo, color etc. Entry and Exit classes manage parkings. Use ArrayList to store parked cars.

20. How can you implement autoboxing and unboxing in your own classes? Autoboxing: Have constructors that take primitive types. Unboxing: Provide get methods that return primitives.

21. How can you find the length of a linked list iteratively and recursively?

Iterative: Initialize length to 0. Traverse linked list and increment length.

Recursive: Length(head) if head == null return 0 else return 1 + length(head.next)

22. How can you find the height of a binary tree in Java? Recursively calculate height of left and right subtrees. Height is max of left height and right height plus 1 for root.

23. How is Bubble Sort algorithm implemented in Java? Compare adjacent elements, swap if currentElement > nextElement. Largest element bubbles up towards end. Repeat until sorted.

24. How can you search for an element in a binary search tree in Java? Start from root and traverse left if element is less than current node otherwise right. Return node if matching element is found.

25. How is Inheritance implemented in Java? Using extends keyword. Single inheritance is supported. Child class inherits properties and methods except private from Parent.

26. How will you implement thread synchronization in Java? 1. Using synchronized keyword 2. Using concurrent collections 3. Using Lock interface 4. Using atomic classes from java.util.concurrent.atomic package

27. How can you avoid deadlock in Java? – Avoid nested locks – Using lock ordering – Using lock timeouts – Avoiding resource sharing between threads

28. How will you store different data types in ArrayList? ArrayList can store only objects. Primitive data types need to be converted to object wrappers like Integer, Character etc.

29. How can you improve performance of ArrayList in Java? Initialise ArrayList with optimal initial capacity to avoid resizing. Use ensureCapacity() before adding large elements to avoid reindexing.

30. How will you implement a HashMap in Java? Use array of LinkedList for chaining. Compute index using hashCode() and compress to fit array. Handle collisions through linked list chaining.

Preparing a strong set of Java interview questions is crucial for aspiring Java developers to successfully clear the technical screening rounds. This collection of 50 Java theory questions and 30 practical scenario-based questions covers a wide range of topics and concepts typically assessed in Java interviews.

Learning the fundamentals and practicing these questions will help candidates master Java programming principles and be able to write code to solve problems. The sample answers provided illustrate how to structure and present your solutions to interviewers to best highlight your Java skills. With thorough preparation on these aspects, developers can confidently tackle Java interview questions and excel in their tech job interviews.

Java Programming Case Study Examples

If you are an HR professional looking for talented Java programmers, then you are in the right place. This article will provide you with some great case study examples that showcase the skills and expertise of top Java programmers.

Importance of Case Studies for HR Professionals

Case studies are an essential tool for HR professionals when hiring top talent. They provide a deeper understanding of a candidate’s skills, knowledge, and experience, which is not always possible through resumes or interviews. By reviewing case studies, HR professionals can evaluate a candidate’s ability to solve complex problems and develop innovative solutions.

Here are some excellent case study examples that demonstrate the skills and expertise of top Java programmers:

Google Maps : Google Maps is one of the most popular navigation applications in the world. It is built using Java and provides real-time traffic updates, street views, and satellite imagery. Google Maps is an excellent example of how Java programming can be used to develop complex and innovative solutions.
Amazon : Amazon is the world’s largest online retailer, and its website is built using Java. The website handles millions of transactions every day, and its success is a testament to the reliability and scalability of Java programming.
Netflix : Netflix is a streaming platform that delivers movies and TV shows to millions of users worldwide. It uses Java programming to create personalized recommendations, manage user profiles, and optimize streaming quality.

Why Choose Algobash?

At Algobash, we specialize in connecting HR professionals with top Java programmers. Our platform features a comprehensive database of talented programmers who have been rigorously tested and vetted. By using Algobash, you can save time and money while finding the perfect candidate for your organization.

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65+ Java advanced interview questions to ask candidates

Java is one of the most popular programming languages that developers use to create back-end development projects – but it does require some skill to navigate.

Due to its complex and intricate design, it’s important to hire a professional who can navigate the language with ease. An effective way to do this is to use skills tests before your interviews.

The Java Coding (Entry-Level) test is perfect for determining whether candidates have sufficient knowledge of coding fundamentals. Once applicants complete the test, you can compare their responses before choosing interview questions – this will help to ensure that you find the perfect candidate for your role.

We’ve created this list of 65+ Java advanced interview questions to help you hire the right candidate.

25 common java advanced interview questions to ask job applicants , 8 sample answers to common java advanced interview questions , 30 tough java advanced interview questions to ask senior programmers and developers , 8 sample answers to tough java advanced interview questions, 14 skill-related java advanced interview questions to hire top talent , 5 sample answers to skill-related java advanced interview questions, when should you use java advanced interview questions in your hiring process , hire technical professionals using java advanced interview questions and skill tests .

Check out these 25 common Java advanced interview questions to ask your candidates at the beginning of each interview.

1. What are Java objects and applications?

2. What is an abstract class?

3. Provide some advantages and disadvantages of Java sockets.

4. What are the different ways you can use a thread?

5. What is a checked and unchecked exception?

6. How do you create an immutable class?

7. What are pass by reference and pass by value?

8. What is the JIT?

9. Does Java support default parameter values?

10. What are the different types of inner classes?

11. What are constructors in Java?

12. Describe object cloning.

13. When can you use the super keyword?

14. What is function overriding and overloading in Java?

15. What are the main differences between array list and vector in Java?

16. Why doesn’t Java use pointers?

17. Explain an infinite loop in Java.

18. What is the difference between exception and error in Java?

19. What is reflection and why is it useful?

20. Can you override a private or static method in Java?

21. What is a marker interface?

22. What do the … dots in the method parameters mean?

23. What are the differences between GET and POST methods?

24. Define a map in Java.

25. What are break and continue statements?

Refer to these answers to common Java interview questions to help you make an informed hiring decision.

8 common Java advanced interview questions graphic

Java objects form when an application executes code. On the other hand, a Java application is a program that developers create using the programming language. Candidates need to understand these basic terms to navigate Java and create dynamic web pages or games.

Use a Java Coding (Data Structures) test to see how candidates run code and effectively work with objects.

2. What are the main differences between array list and vector in Java?

Candidates, whether they’re beginners or seniors, should know how array lists and vectors work in the Java programming language.

These are essential objects that help store elements present in a java.util package. The ideal candidate will provide definitions for both objects before describing their key differences.

For context, an array list can store dynamic elements and change their size according to the package, class, or method. Vectors perform similar actions to array lists, but they synchronize to optimize storage management.

Below you will find the differences between array lists and vectors:

3. Can you override a private or static method in Java?

Experienced candidates will know that overriding a private or static method is not possible. You can’t create a method with the same return type and child class, as it will hide a superclass method.

This method provides access to the parent class when changing the main properties of an excepting object. So, developers won’t be able to override private or static methods since they become inaccessible in a subclass.

4. What are break and continue statements?

Break and continue statements are essential components in Java. Candidates with expert knowledge can explain these actions clearly and describe how they contribute to program development.

A break statement terminates a loop, which is a feature that follows and executes a specific set of instructions. Continue statements only move on to the next iteration of the loop and can skip particular conditions.

5. Define a map in Java.

A map in Java represents the interface of unique keys to values. It is not a subtype of the main collection interface, meaning it has different characteristics when defining a specific value.

Each key and value pair refers to an entry, which is something candidates should understand when using Java maps.

The following are some important aspects of a map:

It doesn’t have duplicate keys

Each key can use one value

6. What is the difference between exception and error in Java?

Errors show when the Java program doesn’t have enough system resources. This means the developer missed an unchecked type when coding. Meanwhile, exceptions only arise during run and compile time. They can disrupt the normal flow of an application if you don’t use the throw keyword.

It’s a good idea to send candidates a Java Coding (Debugging) test before the interview to see how they handle errors and manage exceptions in the programming language.

7. What is the JIT?

The just-in-time compiler (JIT) improves the performance of Java by using the runtime environment to compile bytecodes. These instructions can help a computer run programs with the correct programming language.

Candidates should know that JIT is an integral part of the Java virtual machine, which specifically runs class files through bytecode implementation.

8. How do you create an immutable class?

An immutable class means that developers cannot change its value once they create it. For example, String is a type of immutable class that never changes in the application. To develop this component, you need to:

Declare the class as final so you cannot extend it.

Turn the fields to private to prevent direct access.

Avoid setter methods when creating variables.

Make all mutable fields final so that you can only assign a value once.

Set the value of all fields using the constructor method.

Clone the objects in the getter methods to return a copy instead of an object reference.

Use these 30 tough Java advanced interview questions to evaluate senior candidates’ programming skills , knowledge, and experience with using the Java programming language.

1. Does importing a package import the subpackages as well?

2. What is the difference between compile-time polymorphism and runtime polymorphism?

3. What makes the Java platform independent?

4. Explain the difference between the abstract and final keywords.

5. What is a two-dimensional array? Give some examples of two-dimensional arrays.

6. What are the break and continue statements?

7. Explain the differences between static and default interface methods.

8. What is garbage collection?

9. How can you customize the serialization process?

10. How does an exception permeate through the code?

11. Can you use == on enum?

12. In simple terms, describe a market interface.

13. Differentiate between string, stringbuilder, and stringbuffer in Java.

14. What happens if you write a static public void instead of a public static void?

15. What is the first argument of the string array in the main method?

16. Can you have multiple main methods in the same class?

17. Explain why the Java main method is static.

18. What do you understand about lazy loading in Java?

19. What are the main disadvantages of using garbage collectors in Java?

20. What is the difference between JAR and WAR files?

21. Explain the differences between the prefix and postfix increment operator with a code sample.

22. What are the different types of inheritance in Java?

23. Is there a destructor in Java?

24. What is the difference between applications and applets?

25. Does Java support global variables?

26. What is the difference between a choice and a list?

27. Why is bytecode important in Java?

28. What is the difference between the factory and abstract factory pattern?

29. Define shallow and deep cloning.

30. What is JCA in Java?

Here are some sample answers to tough Java interview questions to determine which candidates best fit the open position.

1. What is the difference between compile-time polymorphism and runtime polymorphism?

Compile-time polymorphism executes all code during compilation. On the other hand, runtime polymorphism can execute the same code but in a more flexible way – it assembles the code when the program runs efficiently.

Candidates should have enough experience to know what these core concepts do in the Java programming language.

2. Explain the differences between the prefix and postfix increment operator with a code sample.

Prefix is the first to perform an increment operation. This process changes the value of variables to ensure they operate on a single command.

A postfix increment operator creates a copy of that object and returns the value from before the increment.

Below is a code sample for prefix:

int n2=++n1;

This code increments n1 and then assigns to n2 automatically. This means that n2 values 11.

The following code is for postfix:

int n2=n1++;

Using this code assigns n2 with the value of n1. Once it obtains that value, the code increments n1 so that n2 shares the same value as 10.

3. What is a two-dimensional array? Give some examples of two-dimensional arrays.

A two-dimensional array is a data structure that uses two subscripts. It has a collection of data in a grid with rows and columns. Candidates may describe it as an array of arrays, which is the most popular description for this component.

The following are some examples of two-dimensional arrays:

int array1[ ][ ] = new int[3][6];

double array2[ ][ ] = new double[2][5];

4. What is garbage collection?

Garbage collection is an automated process that deletes unused code. It can free up memory space and encourage applications to run efficiently, and developers need this process to prevent code overloading or the increased risk of errors.

Those without garbage collection have to implement manual memory management in the coding system themselves.

Use a Clean Code test to determine which candidates can manage and maintain code in Java.

5. Explain the differences between the abstract and final keywords.

Candidates should understand the basics of abstract and final keywords in Java. You can hire top programmers by choosing candidates who provide definitions and clearly state the differences.

The abstract keyword is a non-access modifier, meaning it can create restricted classes. A final keyword makes attributes and methods non-changeable for users. It restricts the user when they perform a specific set of actions.

Below are the key differences between abstract and final keywords:

6. Can you have multiple main methods in the same class?

No, because the program cannot compile all pieces of code. The interviewee could state that the main method is already a defined class. Candidates should answer this question quickly if they have enough knowledge of programming languages.

7. Differentiate between string, stringbuilder, and stringbuffer in Java.

A string is a sequence of characters in Java that represent an object. Developers can manipulate strings through the string class. Strings allow you to examine individual characters in code and compare other objects when writing the source code of a computer program.

The stringbuilder creates objects that developers can modify during development. These string objects are variable-length arrays, which means you can work with a single thread in the programming language.

Stringbuffer, being another type of string, contains a particular sequence of characters that you can change through method calls. Candidates should know that stringbuffers benefit multi-threading in Java because they don’t cause errors.

8. Why is bytecode important in Java?

Bytecode is important in Java because it executes a set of high-quality instructions. This component offers portability and security for the programming language. It also means that developers don’t have to recompile source code for every platform and application.

Here are 14 skill-related Java advanced interview questions to better understand candidates’ Java skills .

1. How would your manager rate your object-oriented programming knowledge?

2. Can you write me a Java program to swap two numbers using the temporary variable?

3. Write a Java program to find the duplicate characters in a string.

4. Give an example of when you had to work with your team to solve a coding problem.

5. Can you overload or override static methods in Java?

6. How do you reverse a string in Java?

7. Write a Java program to show scroll up and scroll down.

8. List some good practices for creating methods in a Java class.

9. Name the different types of Java looping constructs and how you would use them.

10. When do you use an anonymous inner class?

11. Explain how to handle errors using try-catch blocks in your code.

12. How do you optimize code to help improve performance in Java?

13. What is the difference between a thread and a process?

14. List the syntaxes that create a main method for application development in Java.

Use these sample answers to compare candidates’ responses to the skill-related Java advanced interview questions.

5 skill related Java advanced interview questions graphic

This question gives you insight into the candidate’s personality and skills. They should tell you what they know about objects in Java and how to create them using specific actions and clean code. You can determine which candidates are honest when it comes to their programming strengths and weaknesses.

Send candidates an Object-Oriented Programming test to see how they solve programming tasks and create objects using effective and clean code.

2. Explain how to handle errors using try-catch blocks in your code.

The candidate should show their programming skills by explaining what the try-catch method is and how it works when catching errors.

This method defines a block of code that may comprise errors and exceptions. A professional developer will place the default code in a try block and run the program to detect any potential defects.

Candidates can also mention the following code:

// code…

} catch (err) {

// error handling

3. Give an example of when you had to work with your team to solve a coding problem.

Candidates should provide an example of a problem they faced in a previous job. Their answer determines their problem-solving skills and ability to communicate with others.

For instance, one candidate might discuss how a syntax error stopped the application from running. To solve this problem, they used the try-catch block with other team members to find the grammatical error in the code.

Use a Problem-Solving test to see how candidates approach complex problems when coding in Java. You can also determine whether they have the skills to execute code properly and solve common errors.

4. Can you write me a Java program to swap two numbers using the temporary variable?

This is more of a practical question that may challenge candidates’ knowledge – give them a computer to write the code and see what they can come up with.

A temporary variable has a short lifetime since developers will discard it after implementing code. This short-lived component can still benefit the switch between two numbers in a Java program.

The following are some steps and a coding example for swapping the numbers:

Assign value of x to temp

Assign value of y to x

Assign value of temp to y

public class Main

public static void main(String[] args)

int temp;

int x = 200;

int y = 300;

//Swapping in steps

temp = x;

x = y;

y = temp;

//Verify swapped values

System.out.println(“x = ” + x + ” and y = ” + y);

Candidates with a similar example probably have more experience with using Java and writing complex code.

5. Write a Java program to show scroll up and scroll down.

Using another practical skill-related question can help you narrow down your list of candidates during the interview. They should be eager to answer and show their knowledge of designing code in a Java application.

For scrolling down:

WebDriver driver = new FirefoxDriver();

JavascriptExecutor jse = (JavascriptExecutor)driver;

jse.executeScript(“window.scrollBy(0,250)”);

For scrolling up:

jse.executeScript(“window.scrollBy(0,-250)”);

jse.executeScript(“scroll(0, -250);”);

Since most developers use Selenium to design code in Java, you can send candidates a Selenium with Python test . This assessment determines their ability to run automation and testing while writing code in different environments.

Before you use specific interview questions, make sure you take advantage of skills tests first. These pre-employment assessments can help you screen candidates without having to scan through hundreds of job applications, saving you precious time, and ensuring that you only interview the very best candidates.

By incorporating skill tests into your hiring process, you can:

Bridge internal skill gaps

Reduce unconscious bias when hiring

Save recruitment time and costs

Enhance employer branding

Engage more with candidates

Hire the right person for the job

Be sure to choose skill tests that relate to the open position in your company. For example, you might use an Attention to Detail test to find candidates who can notice coding mistakes or identify potential weaknesses in a programming language.

Our test library can provide you with data-driven tests that enhance your hiring process. You can choose a skill assessment according to your open position and recruitment needs. These tests range from programming skills to cognitive function, so you have plenty of options.

Do you want to learn more?

Book a free 30-minute demo to join a live chat about the benefits of skill tests and how you can use them to hire talented professionals. Alongside this, you will also get a chance to ask questions about your own employment strategy.

Find a talented programmer or developer using our skill tests and Java advanced interview questions. Sign up for your free plan today .

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21 Essential Java Interview Questions *

Toptal sourced essential questions that the best java developers and engineers can answer. driven from our community, we encourage experts to submit questions and offer feedback..

Interview Questions

Describe and compare fail-fast and fail-safe iterators. Give examples.

The main distinction between fail-fast and fail-safe iterators is whether or not the collection can be modified while it is being iterated. Fail-safe iterators allow this; fail-fast iterators do not.

Fail-fast iterators operate directly on the collection itself. During iteration, fail-fast iterators fail as soon as they realize that the collection has been modified (i.e., upon realizing that a member has been added, modified, or removed) and will throw a ConcurrentModificationException . Some examples include ArrayList , HashSet , and HashMap (most JDK1.4 collections are implemented to be fail-fast).

Fail-safe iterates operate on a cloned copy of the collection and therefore do not throw an exception if the collection is modified during iteration. Examples would include iterators returned by ConcurrentHashMap or CopyOnWriteArrayList .

ArrayList , LinkedList , and Vector are all implementations of the List interface. Which of them is most efficient for adding and removing elements from the list? Explain your answer, including any other alternatives you may be aware of.

Of the three, LinkedList is generally going to give you the best performance. Here’s why:

ArrayList and Vector each use an array to store the elements of the list. As a result, when an element is inserted into (or removed from) the middle of the list, the elements that follow must all be shifted accordingly. Vector is synchronized, so if a thread-safe implementation is not needed, it is recommended to use ArrayList rather than Vector.

LinkedList , on the other hand, is implemented using a doubly linked list. As a result, an inserting or removing an element only requires updating the links that immediately precede and follow the element being inserted or removed.

However, it is worth noting that if performance is that critical, it’s better to just use an array and manage it yourself, or use one of the high performance 3rd party packages such as Trove or HPPC .

Why would it be more secure to store sensitive data (such as a password, social security number, etc.) in a character array rather than in a String?

In Java, Strings are immutable and are stored in the String pool. What this means is that, once a String is created, it stays in the pool in memory until being garbage collected. Therefore, even after you’re done processing the string value (e.g., the password), it remains available in memory for an indeterminate period of time thereafter (again, until being garbage collected) which you have no real control over. Therefore, anyone having access to a memory dump can potentially extract the sensitive data and exploit it.

In contrast, if you use a mutable object like a character array, for example, to store the value, you can set it to blank once you are done with it with confidence that it will no longer be retained in memory.

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What is the ThreadLocal class? How and why would you use it?

A single ThreadLocal instance can store different values for each thread independently. Each thread that accesses the get() or set() method of a ThreadLocal instance is accessing its own, independently initialized copy of the variable. ThreadLocal instances are typically private static fields in classes that wish to associate state with a thread (e.g., a user ID or transaction ID). The example below, from the ThreadLocal Javadoc , generates unique identifiers local to each thread. A thread’s id is assigned the first time it invokes ThreadId.get() and remains unchanged on subsequent calls.

Each thread holds an implicit reference to its copy of a thread-local variable as long as the thread is alive and the ThreadLocal instance is accessible; after a thread goes away, all of its copies of thread-local instances are subject to garbage collection (unless other references to these copies exist).

What is the volatile keyword? How and why would you use it?

In Java, each thread has its own stack, including its own copy of variables it can access. When the thread is created, it copies the value of all accessible variables into its own stack. The volatile keyword basically says to the JVM “Warning, this variable may be modified in another Thread”.

In all versions of Java, the volatile keyword guarantees global ordering on reads and writes to a variable. This implies that every thread accessing a volatile field will read the variable’s current value instead of (potentially) using a cached value.

In Java 5 or later, volatile reads and writes establish a happens-before relationship, much like acquiring and releasing a mutex.

Using volatile may be faster than a lock, but it will not work in some situations. The range of situations in which volatile is effective was expanded in Java 5; in particular, double-checked locking now works correctly.

The volatile keyword is also useful for 64-bit types like long and double since they are written in two operations. Without the volatile keyword you risk stale or invalid values.

One common example for using volatile is for a flag to terminate a thread. If you’ve started a thread, and you want to be able to safely interrupt it from a different thread, you can have the thread periodically check a flag (i.e., to stop it, set the flag to true ). By making the flag volatile, you can ensure that the thread that is checking its value will see that it has been set to true without even having to use a synchronized block. For example:

Compare the sleep() and wait() methods in Java, including when and why you would use one vs. the other.

sleep() is a blocking operation that keeps a hold on the monitor / lock of the shared object for the specified number of milliseconds.

wait() , on the other hand, simply pauses the thread until either (a) the specified number of milliseconds have elapsed or (b) it receives a desired notification from another thread (whichever is first), without keeping a hold on the monitor/lock of the shared object.

sleep() is most commonly used for polling, or to check for certain results, at a regular interval. wait() is generally used in multithreaded applications, in conjunction with notify() / notifyAll() , to achieve synchronization and avoid race conditions.

Tail recursion is functionally equivalent to iteration. Since Java does not yet support tail call optimization, describe how to transform a simple tail recursive function into a loop and why one is typically preferred over the other.

Here is an example of a typical recursive function, computing the arithmetic series 1, 2, 3…N. Notice how the addition is performed after the function call. For each recursive step, we add another frame to the stack.

Tail recursion occurs when the recursive call is in the tail position within its enclosing context - after the function calls itself, it performs no additional work. That is, once the base case is complete, the solution is apparent. For example:

Here you can see that a plays the role of the accumulator - instead of computing the sum on the way down the stack, we compute it on the way up, effectively making the return trip unnecessary, since it stores no additional state and performs no further computation. Once we hit the base case, the work is done - below is that same function, “unrolled”.

Many functional languages natively support tail call optimization, however the JVM does not. In order to implement recursive functions in Java, we need to be aware of this limitation to avoid StackOverflowError s. In Java, iteration is almost universally preferred to recursion.

How can you swap the values of two numeric variables without using any other variables?

You can swap two values a and b without using any other variables as follows:

How can you catch an exception thrown by another thread in Java?

This can be done using Thread.UncaughtExceptionHandler .

Here’s a simple example:

What is the Java Classloader? List and explain the purpose of the three types of class loaders.

The Java Classloader is the part of the Java runtime environment that loads classes on demand (lazy loading) into the JVM (Java Virtual Machine). Classes may be loaded from the local file system, a remote file system, or even the web.

When the JVM is started, three class loaders are used: 1. Bootstrap Classloader: Loads core java API file rt.jar from folder. 2. Extension Classloader: Loads jar files from folder. 3. System/Application Classloader: Loads jar files from path specified in the CLASSPATH environment variable.

Is a finally block executed when an exception is thrown from a try block that does not have a catch block, and if so, when?

A finally block is executed even if an exception is thrown or propagated to the calling code block.

Output can vary, being either:

When designing an abstract class, why should you avoid calling abstract methods inside its constructor?

This is a problem of initialization order. The subclass constructor will not have had a chance to run yet and there is no way to force it to run it before the parent class. Consider the following example class:

This seems like a good start for an abstract Widget: it allows subclasses to fill in width and height , and caches their initial values. However, look when you spec out a typical subclass implementation like so:

Now we’ve introduced a subtle bug: Widget.cachedWidth and Widget.cachedHeight will always be zero for SquareWidget instances! This is because the this.size = size assignment occurs after the Widget constructor runs.

Avoid calling abstract methods in your abstract classes’ constructors, as it restricts how those abstract methods can be implemented.

What variance is imposed on generic type parameters? How much control does Java give you over this?

Java’s generic type parameters are invariant . This means for any distinct types A and B , G<A> is not a subtype or supertype of G<B> . As a real world example, List<String> is not a supertype or subtype of List<Object> . So even though String extends (i.e. is a subtype of) Object , both of the following assignments will fail to compile:

Java does give you some control over this in the form of use-site variance . On individual methods, we can use ? extends Type to create a covariant parameter. Here’s an example:

Even though longs is a List<Long> and not List<Number> , it can be passed to sum .

Similarly, ? super Type lets a method parameter be contravariant . Consider a function with a callback parameter:

forEachNumber allows Callback<Object> to be a subtype of Callback <Number> , which means any callback that handles a supertype of Number will do:

Note, however, that attempting to provide a callback that handles only Long (a subtype of Number ) will rightly fail:

Liberal application of use-site variance can prevent many of the unsafe casts that often appear in Java code and is crucial when designing interfaces used by multiple developers.

What are static initializers and when would you use them?

A static initializer gives you the opportunity to run code during the initial loading of a class and it guarantees that this code will only run once and will finish running before your class can be accessed in any way.

They are useful for performing initialization of complex static objects or to register a type with a static registry, as JDBC drivers do.

Suppose you want to create a static, immutable Map containing some feature flags. Java doesn’t have a good one-liner for initializing maps, so you can use static initializers instead:

Within the same class, you can repeat this pattern of declaring a static field and immediately initializing it, since multiple static initializers are allowed.

If one needs a Set , how do you choose between HashSet vs. TreeSet ?

At first glance, HashSet is superior in almost every way: O(1) add , remove and contains , vs. O(log(N)) for TreeSet .

However, TreeSet is indispensable when you wish to maintain order over the inserted elements or query for a range of elements within the set.

Consider a Set of timestamped Event objects. They could be stored in a HashSet , with equals and hashCode based on that timestamp. This is efficient storage and permits looking up events by a specific timestamp, but how would you get all events that happened on any given day? That would require a O(n) traversal of the HashSet , but it’s only a O(log(n)) operation with TreeSet using the tailSet method:

If Event happens to be a class that we cannot extend or that doesn’t implement Comparable , TreeSet allows us to pass in our own Comparator :

Generally speaking, TreeSet is a good choice when order matters and when reads are balanced against the increased cost of writes.

What are method references, and how are they useful?

Method references were introduced in Java 8 and allow constructors and methods (static or otherwise) to be used as lambdas. They allow one to discard the boilerplate of a lambda when the method reference matches an expected signature.

For example, suppose we have a service that must be stopped by a shutdown hook. Before Java 8, we would have code like this:

With lambdas, this can be cut down considerably:

However, stop matches the signature of Runnable.run ( void return type, no parameters), and so we can introduce a method reference to the stop method of that specific SomeBusyService instance:

This is terse (as opposed to verbose code) and clearly communicates what is going on.

Method references don’t need to be tied to a specific instance, either; one can also use a method reference to an arbitrary object, which is useful in Stream operations. For example, suppose we have a Person class and want just the lowercase names of a collection of people:

A complex lambda can also be pushed into a static or instance method and then used via a method reference instead. This makes the code more reusable and testable than if it were “trapped” in the lambda.

So we can see that method references are mainly used to improve code organization, clarity and terseness.

How are Java enums more powerful than integer constants? How can this capability be used?

Enums are essentially final classes with a fixed number of instances. They can implement interfaces but cannot extend another class.

This flexibility is useful in implementing the strategy pattern, for example, when the number of strategies is fixed. Consider an address book that records multiple methods of contact. We can represent these methods as an enum and attach fields, like the filename of the icon to display in the UI, and any corresponding behaviour, like how to initiate contact via that method:

We can dispense with switch statements entirely by simply using instances of ContactMethod :

This is just the beginning of what can be done with enums. Generally, the safety and flexibility of enums means they should be used in place of integer constants, and switch statements can be eliminated with liberal use of abstract methods.

What does it mean for a collection to be “backed by” another? Give an example of when this property is useful.

If a collection backs another, it means that changes in one are reflected in the other and vice-versa.

For example, suppose we wanted to create a whitelist function that removes invalid keys from a Map . This is made far easier with Map.keySet , which returns a set of keys that is backed by the original map. When we remove keys from the key set, they are also removed from the backing map:

retainAll writes through to the backing map, and allows us to easily implement something that would otherwise require iterating over the entries in the input map, comparing them against allowedKey , etcetera.

Note, it is important to consult the documentation of the backing collection to see which modifications will successfully write through. In the example above, map.keySet().add(value) would fail, because we cannot add a key to the backing map without a value.

What is reflection? Give an example of functionality that can only be implemented using reflection.

Reflection allows programmatic access to information about a Java program’s types. Commonly used information includes: methods and fields available on a class, interfaces implemented by a class, and the runtime-retained annotations on classes, fields and methods.

Examples given are likely to include:

Annotation-based serialization libraries often map class fields to JSON keys or XML elements (using annotations). These libraries need reflection to inspect those fields and their annotations and also to access the values during serialization.
Model-View-Controller frameworks call controller methods based on routing rules. These frameworks must use reflection to find a method corresponding to an action name, check that its signature conforms to what the framework expects (e.g. takes a Request object, returns a Response ), and finally, invoke the method.
Dependency injection frameworks lean heavily on reflection. They use it to instantiate arbitrary beans for injection, check fields for annotations such as @Inject to discover if they require injection of a bean, and also to set those values.
Object-relational mappers such as Hibernate use reflection to map database columns to fields or getter/setter pairs of a class, and can go as far as to infer table and column names by reading class and getter names, respectively.

A concrete code example could be something simple, like copying an object’s fields into a map:

Such tricks can be useful for debugging, or for utility methods such as a toString method that works on any class.

Aside from implementing generic libraries, direct use of reflection is rare but it is still a handy tool to have. Knowledge of reflection is also useful for when these mechanisms fail.

However, it is often prudent to avoid reflection unless it is strictly necessary, as it can turn straightforward compiler errors into runtime errors.

Nested classes can be static or non-static (also called an inner class). How do you decide which to use? Does it matter?

The key difference between is that inner classes have full access to the fields and methods of the enclosing class. This can be convenient for event handlers, but comes at a cost: every instance of an inner class retains and requires a reference to its enclosing class.

With this cost in mind, there are many situations where we should prefer static nested classes. When instances of the nested class will outlive instances of the enclosing class, the nested class should be static to prevent memory leaks. Consider this implementation of the factory pattern:

At a glance, this design looks good: the WidgetParserFactory hides the implementation details of the parser with the nested class WidgetParserImpl . However, WidgetParserImpl is not static, and so if WidgetParserFactory is discarded immediately after the WidgetParser is created, the factory will leak, along with all the references it holds.

WidgetParserImpl should be made static, and if it needs access to any of WidgetParserFactory ’s internals, they should be passed into WidgetParserImpl ’s constructor instead. This also makes it easier to extract WidgetParserImpl into a separate class should it outgrow its enclosing class.

Inner classes are also harder to construct via reflection due to their “hidden” reference to the enclosing class, and this reference can get sucked in during reflection-based serialization, which is probably not intended.

So we can see that the decision of whether to make a nested class static is important, and that one should aim to make nested classes static in cases where instances will “escape” the enclosing class or if reflection on those nested classes is involved.

What is the difference between String s = "Test" and String s = new String("Test") ? Which is better and why?

In general, String s = "Test" is more efficient to use than String s = new String("Test") .

In the case of String s = "Test" , a String with the value “Test” will be created in the String pool. If another String with the same value is then created (e.g., String s2 = "Test" ), it will reference this same object in the String pool.

However, if you use String s = new String("Test") , in addition to creating a String with the value “Test” in the String pool, that String object will then be passed to the constructor of the String Object (i.e., new String("Test") ) and will create another String object (not in the String pool) with that value. Each such call will therefore create an additional String object (e.g., String s2 = new String("Test") would create an addition String object, rather than just reusing the same String object from the String pool).

There is more to interviewing than tricky technical questions, so these are intended merely as a guide. Not every “A” candidate worth hiring will be able to answer them all, nor does answering them all guarantee an “A” candidate. At the end of the day, hiring remains an art, a science — and a lot of work .

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Core Java Interview Questions

We've developed a list of Advanced Core Java Interview Questions to assist you ace your interview and land your ideal job as a Core Java Developer.

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Experienced

If you're looking for Core Java Interview Questions & Answers for Experienced or Freshers, you are at the right place. There are a lot of opportunities from many reputed companies in the world. According to research Core Java has a market share of about 10.1%.

So, You still have the opportunity to move ahead in your career in Core Java Development. Mindmajix offers Advanced Core Java Interview Questions 2024 that help you in cracking your interview & acquire a dream career as Core Java Developer.

We have categorized Core Java Interview Questions into 2 levels they are:

Frequently Asked Core Java Interview Questions

What are the principle concepts of OOPS?
What is Encapsulation?
What is the difference between Abstraction and Encapsulation?
What is Polymorphism?
Explain the different forms of Polymorphism.
What is Dynamic Binding?
What is method overriding?
What is the difference between method overloading and method overriding?
Is it possible to override the main method?
How do you prevent a method from being overridden?

Core Java Interview Questions For Freshers

1. what are the principle concepts of oops.

There are four principle concepts upon which object-oriented design and programming rest. They are:

Abstraction
Polymorphism
Inheritance
Encapsulation.

(i.e. easily remembered as A-PIE).

2. What is Abstraction?

Abstraction refers to the act of representing essential features without including the background details or explanations.

3. What is Encapsulation?

Encapsulation is a technique used for hiding the properties and behaviors of an object and allowing outside access only as appropriate. It prevents other objects from directly altering or accessing the properties or methods of the encapsulated object.

[ Learn Complete Java Tutorial ]

4. What is the difference between Abstraction and Encapsulation?

Abstraction focuses on the outside view of an object (i.e. the interface) Encapsulation (information hiding) prevents clients from seeing its inside view, where the behavior of the abstraction is implemented.

Abstraction solves the problem on the design side while Encapsulation is the Implementation.
Encapsulation is the deliverables of Abstraction. Encapsulation barely talks about grouping up your abstraction to suit the developer's needs.

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5. What is Inheritance?

Inheritance is the process by which objects of one class acquire the properties of objects of another class. A class that is inherited is called a superclass. The class that does the inheriting is called a subclass. Inheritance is done by using the keyword extends.

The two most common reasons to use inheritance are:

To promote code reuse
To use polymorphism.

[ Check out Data Types in Java ]

6. What is Polymorphism?

Polymorphism is briefly described as “one interface, many implementations.” Polymorphism usage to something in different contexts – specifically, to allow an entity such as a variable, a function, or an object to have more than one form.

7. How does Java implement polymorphism?

Inheritance, Overloading, and Overriding are used to achieve Polymorphism in Java. Polymorphism manifests itself in Java in the form of multiple methods having the same name.

In some cases, multiple methods have the same name, but different formal argument lists (overloaded methods). In other cases, multiple methods have the same name, same return type, and the same formal argument list (overridden methods).

8. Explain the different forms of Polymorphism.

There are two types of polymorphism, one is Compile time polymorphism and the other is run time polymorphism. Compile-time polymorphism is method overloading. Runtime time polymorphism is done using inheritance and interface.

Note : From a practical programming viewpoint, polymorphism manifests itself in three distinct forms in Java:

Method overloading
Method overriding through inheritance
Method overriding through the Java interface.

[ Check out Top Java EE Frameworks ]

9. What is runtime polymorphism or dynamic method dispatch?

In Java, runtime polymorphism or dynamic method dispatch is a process in which a call to an overridden method is resolved at runtime rather than at compile time. In this process, an overridden method is called through the reference variable of a superclass. The determination of the method to be called is based on the object being referred to by the reference variable.

10. What is Dynamic Binding?

Binding refers to the linking of a procedure call to the code to be executed in response to the call. Dynamic binding (also known as late binding) means that the code associated with a given procedure call is not known until the time of the call at run-time. It is associated with polymorphism and inheritance.

11. What is method overloading?

Method Overloading means having two or more methods with the same name in the same class with different arguments. The benefit of method overloading is that it allows you to implement methods that support the same semantic operation but differ by argument number or type.

Important Note:

Overloaded methods MUST change the argument list.
Overloaded methods CAN change the return type.
Overloaded methods CAN change the access modifier.
Overloaded methods CAN declare new or broader checked exceptions.
A method can be overloaded in the same class or in a subclass.

12. What is method overriding?

Method overriding occurs when a subclass declares a method that has the same type of arguments as a method declared by one of its superclasses. The key benefit of overriding is the ability to define behavior that’s specific to a particular subclass type.

Note : The overriding method cannot have a more restrictive access modifier than the method being overridden (Ex: You can’t override a method marked public and make it protected). You cannot override a method marked final. You cannot override a method marked Static.

[ A Complete Guide to Control Statements in Java ]

Core Java Interview Questions for Experienced

13. what is the difference between method overloading and method overriding.

Overloaded Method:

Arguments – Must Change
Return type: Can Change
Exceptions – Can Change
Access – Can Change
Invocation – Reference type determines which overloaded version is selected. Happens at compile time.

Overridden Method:

Arguments – Must not Change
Return type: Can’t change except for covariant returns
Exceptions – Can reduce or eliminate. Must not throw new or broader checked exceptions
Access – Must not make more restrictive (can be less restrictive)
Invocation – Object type determines which method is selected. Happens at runtime.

14. Can overloaded methods be overridden too?

Yes, derived classes still can override the overloaded methods. Polymorphism can still happen. The compiler will not be binding the method calls since it is overloaded, because it might be overridden now or in the future.

15. Is it possible to override the main method?

No, because the main is a Static method. A Static method can’t be overridden in Java.

16. How to invoke a superclass version of an Overridden method?

To invoke a superclass method that has been overridden in a subclass, you must either call the method directly through a superclass instance or use the super prefix in the subclass itself. From the point of view of the subclass, the super prefix provides an explicit reference to the superclass’s implementation of the method.

17. What is Super?

Super is a keyword that is used to access the method or member variables from the superclass. If a method hides one of the member variables in its superclass, the method can refer to the hidden variable through the use of the super keyword. In the same way, if a method overrides one of the methods in its superclass, the method can invoke the overridden method through the use of the super keyword.

Note: You can only go back to one level. In the constructor, if you use super(), it must be the very first code, and you cannot access any of these. xxx variables or methods to compute its parameters.

18. How do you prevent a method from being overridden?

To prevent a specific method from being overridden in a subclass, use the final modifier on the method declaration, which means “this is the final implementation of this method”, the end of its inheritance hierarchy.

19. What is an Interface?

An interface is a description of a set of methods that conform to implementing classes must-haves.

You can’t mark an interface as final.
Interface variables must be Static.
An Interface cannot extend anything but another interface.

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Ravindra Savaram is a Technical Lead at Mindmajix.com . His passion lies in writing articles on the most popular IT platforms including Machine learning, DevOps, Data Science, Artificial Intelligence, RPA, Deep Learning, and so on. You can stay up to date on all these technologies by following him on LinkedIn and Twitter .

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13.5: Case Study- Designing a Basic GUI

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Ralph Morelli & Ralph Wade
Trinity College

What elements make up a basic user interface? If you think about all of the various interfaces you’ve encountered—and don’t just limit yourself to computers—they all have the following elements:

Some way to provide help/guidance to the user.

Some way to allow input of information.

Some way to allow output of information.

Some way to control the interaction between the user and the device.

Think about the interface on a beverage machine. Printed text on the machine will tell you what choices you have, where to put your money, and what to do if something goes wrong. The coin slot is used to input money. There’s often some kind of display to tell you how much money you’ve inserted. And there’s usually a bunch of buttons and levers that let you control the interaction with the machine.

These same kinds of elements make up the basic computer interface. Designing a Graphical User Interface is primarily a process of choosing components that can effectively perform the tasks of input, output, control, and guidance.

In the programs we designed in the earlier chapters, we used two different kinds of interfaces. In the command-line interface, we used printed prompts to inform the user, typed commands for data entry and user control, and printed output to report results. Our GUI interfaces used JLabel s to guide and prompt the user, JTextField s and JTextArea s as basic input and output devices, and either JButton s or JTextField s for user control.

Let’s begin by building a basic GUI in the form of a Java application. To keep the example as close as possible to the GUIs we’ve already used, we will build it out of the following Swing components: JLabel , JTextField , JTextArea , and JButton .

The Metric Converter Application

Suppose the coach of the cross-country team asks you to write a Java application that can be used to convert miles to kilometers. The program should let the user input a distance in miles, and the program should report the equivalent distance in kilometers.

Before we design the interface for this, let’s first define a MetricConverter class that can be used to perform the conversions (Fig. 13.9). For now at least, this class’s only task will be to convert miles to kilometers, for which it will use the formula that 1 kilometer equals 0.62 miles:

Note that the method takes a double as input and returns a double . Also, by declaring the method static , we make it a class method, so it can be invoked simply by

Choosing the Components

Let’s now design a GUI to handle the interaction with the user. First, let’s choose Swing components for each of the four interface tasks of input, output, control, and guidance. For each component, it might be useful to refer back to Figure [fig-swing2-guis] to note its location in the Swing hierarchy.

A JLabel is a display area for a short string of text, an image, or both. Its AWT counterpart, the Label , cannot display images. A does not react to input. Therefore, it is used primarily to display a graphic or small amounts of static text. It is perfectly suited to serve as a prompt, which is what we will use it for in this interface.

A JTextField is a component that allows the user to edit a single line of text. It is identical to its AWT counterpart, the TextField . By using its getText() and setText() methods, a JTextField can be used for either input or output, or both. For this problem, we’ll use it to perform the interface’s input task.

A JTextArea is a multiline text area that can be used for either input or output. It is almost identical to the AWT TextArea component. One difference, however, is that a JTextArea does not contain scrollbars by default. For this program, we’ll use the JTextArea for displaying the results of conversions. Because it is used solely for output in this program, we’ll make it uneditable to prevent the user from typing in it.

Let’s use a JButton as our main control for this interface. By implementing the ActionListener interface we will handle the user’s action events.

Choosing the Top-Level Window

The next issue we must decide is what kind of top-level window to use for this interface. For applet interfaces, the top-level component would be a JApplet . For Java applications, you would typically use a JFrame as the top-level window. Both of these classes are subclasses of Container , so they are suitable for holding the components that make up the interface (Fig. [fig-swing1-guis] ).

Also, as noted earlier, JApplet s and JFrame s are both examples of heavyweight components, so they both have windows associated with them. To display a JFrame we just have to give it a size and make it visible. Because a frame runs as a stand-alone window, not within a browser context, it should also be able to exit the application when the user closes the frame.

Designing a Layout

The next step in designing the interface is deciding how to arrange the components so that they will be visually appealing and comprehensible, as well as easy to use.

Figure [fig-metricgui] shows a design for the layout. The largest component is the output text area, which occupies the center of the JFrame . The prompt, input text field, and control button are arranged in a row above the text area. This is a simple and straightforward layout.

Figure [fig-metricgui] also provides a containment hierarchy , also called a widget hierarchy , which shows the containment relationships among the various components. Although it might not seem so for this simple layout, the containment hierarchy plays an important role in showing how the various components are grouped in the interface. For this design, we have a relatively simple hierarchy, with only one level of containment. All of the components are contained directly in the JFrame .

Figure 13.11 shows the design of the Converter class, which extends the JFrame class and implements the ActionListener interface. As a JFrame subclass, a Converter can contain GUI components. As an implementor of the ActionListener interface, it also will be able to handle action events through the actionPerformed() method.

Figure [fig-converterclass] gives the implementation of the Converter class. Note the three packages that are imported. The first contains definitions of the Swing classes, and the other two contain definitions of AWT events and layout managers that are used in the program.

We have to do all initializing tasks in the constructor. First, we have to set the JFrame ’s layout to FlowLayout . A layout manager is the object that is responsible for sizing and arranging the components in a container so that the elements are organized in the best possible manner. A flow layout is the simplest arrangement: The components are arranged left to right in the window, wrapping around to the next “row” if necessary.

Second, note the statements used to set the layout and to add components directly to the JFrame . Instead of adding components directly to the JFrame , we must add them to its content pane:

A content pane is a JPanel that serves as the working area of the JFrame . It contains all of the frame’s components. Java will raise an exception if you attempt to add a component directly to a JFrame .

The JFrame and all the other top-level Swing windows have an internal structure made up of several distinct objects that can be manipulated by the program. Because of this structure, GUI elements can be organized into different layers within the window to create many types of sophisticated layouts. Also, one layer of the structure makes it possible to associate a menu with the frame.

Finally, note how the Converter frame is instantiated, made visible, and eventually exited in the application’s main() method:

It is necessary to set both the size and visibility of the frame, since these are not set by default. Because we are using a FlowLayout , it is especially important to give the frame an appropriate size. Failure to do so can cause the components to be arranged in a confusing way and might even cause some components to not appear in the window. These are limitations we will fix when we learn how to use some of the other layout managers.

Inner Classes and Adapter Classes

In this section we introduce two new language features, inner classes and adapter classes , which are used in the main() method shown above to handle the closing of the Converter application’s window when the program is exited:

This code segment provides a listener that listens for window closing events. When such an event occurs, it exits the application by calling System.exit() .

The syntax used here is an example of an anonymous inner class . An inner class is a class defined within another class. The syntax is somewhat ugly, because it places the class definition right where a reference to a window listener object would go. In effect what the code is doing is defining a subclass of WindowAdapter and creating an instance of it to serve as a listener for window closing events.

Anonymous inner classes provide a useful way of creating classes and objects on the fly to handle just this kind of listener task. The syntax used actually enables us to write one expression that both defines a class and creates an instance of it to listen for window closing events. The new subclass has local scope limited here to the main() method. It is anonymous, meaning we aren’t even giving it a name, so you can’t create other instances of it in the program. Note that the body of the class definition is placed right after the new keyword, which takes the place of the argument to the addWindowListener() method. For more details on the inner and anonymous classes, see Appendix F.

An adapter class is a wrapper class that implements trivial versions of the abstract methods that make up a particular interface. (Remember from Chapter 4 that a wrapper class contains methods for converting primitive data into objects and for converting data from one type to another.)

The WindowAdapter class implements the methods of the WindowListener interface. When you implement an interface, such as ActionListener , you must implement all the abstract methods defined in the interface. For ActionListener there’s just one method, the actionPerformed() method, so we can implement it as part of our applet or frame class. However, we want to use only one of the seven methods available in the WindowListener interface, the windowClosing() method, which is the method implemented in the anonymous inner class:

The WindowAdapter is defined simply as

Note that each method is given a trivial implementation (). To create a subclass of WindowAdapter , you must override at least one of its trivially implemented methods.

Another way to manage the application’s window closing event is to define a subclass of WindowAdapter :

Given this class, we can then place the following statement in Converter ’s main() method:

This is somewhat more familiar looking than the inner class construct. If you prefer this way of handling things, you can use this method in place of the inner classes here and in other examples.

GUI Design Critique

Figure 13.13 shows the converter interface. Although our basic GUI design satisfies the demands of input, output, control, and guidance, it has a few significant design flaws.

First, it forces the user to manually clear the input field after each conversion. Unless it is important that the user’s input value remain displayed until another value is entered, this is just an inconvenience to the user. In this case, the user’s input value is displayed along with the result in the JTextArea , so there’s no reason not to clear the input text field:

A second problem with our design is that it forces the user to switch between the keyboard (for input) and the mouse (for control). Experienced users will find this annoying. An easy way to fix this problem is to make both the JTextField and the JButton serve as controls. That way, to get the program to do the conversion, the user can just press the Enter key after typing a number into the text field.

To give the interface this type of control, we only need to add an ActionListener to the JTextField during the initialization step:

A JTextField generates an ActionEvent whenever the Enter key is pressed. We don’t even need to modify the actionPerformed() method, since both controls will generate the same action event. This will allow users who prefer the keyboard to use just the keyboard.

Given that the user can now interact with the interface with just the keyboard, a question arises over whether we should keep the button at all. In this case, it seems justifiable to keep both the button and the text field controls. Some users dislike typing and prefer to use the mouse. Also, having two independent sets of controls is a desirable form of redundancy. You see it frequently in menu-based systems that allow menu items to be selected either by mouse or by special control keys.

Another deficiency in the converter interface is that it doesn’t round off its result, leading sometimes to numbers with 20 or so digits. Develop Java code to fix this problem.

Give an example of desirable redundancy in automobile design.

Extending the Basic GUI: Button Array

Suppose the coach likes our program but complains that some of the folks in the office are terrible typists and would prefer not to have to use the keyboard at all. Is there some way we could modify the interface to accommodate these users?

This gets back to the point we were just making about incorporating redundancy into the interface. One way to satisfy this requirement would be to implement a numeric keypad for input, similar to a calculator keypad. Regular JButton s can be used as the keypad’s keys. As a user clicks keypad buttons, their face values—0 through 9—are inserted into the text field. The keypad will also need a button to clear the text field and one to serve as a decimal point.

This new feature will add 12 new JButton components to our interface. Instead of inserting them into the JFrame individually, it will be better to organize them into a separate panel and to insert the entire panel into the frame as a single unit. This will help reduce the complexity of the display, especially if the keypad buttons can be grouped together visually. Instead of having to deal with 16 separate components, the user will see the keypad as a single unit with a unified function. This is an example of the abstraction principle, similar to the way we break long strings of numbers (1-888-889-1999) into subgroups to make them easier to remember.

Figure [fig-metricgui2] shows the revised converter interface design. The containment hierarchy shows that the 12 keypad JButton s are contained within a JPanel . In the frame’s layout, the entire panel is inserted just after the text area.

Incorporating the keypad into the interface requires several changes in the program’s design. Because the keypad has such a clearly defined role, let’s make it into a separate object by defining a KeyPad class (Fig. 13.15). The KeyPad will be a subclass of JPanel and will handle its own ActionEvent s. As we saw in Chapter 4, a JPanel is a generic container. It is a subclass of Container via the JComponent class (Fig. [fig-swing2-guis] ). Its main purpose is to contain and organize components that appear together on an interface.

In this case, we will use a JPanel to hold the keypad buttons. As you might recall from Chapter 4, to add elements to a JPanel , you use the add() method, which is inherited from Container . (A JApplet is also a subclass of Container via the Panel class.)

As a subclass of JPanel , the KeyPad will take care of holding and organizing the JButton s in the visual display. We also need some way to organize and manage the 12 keypad buttons within the program’s memory. Clearly, this is a good job for an array. Actually, two arrays would be even better, one for the buttons and one for their labels:

The label array stores the strings that we will use as the buttons’ labels. The main advantage of the array is that we can use a loop to instantiate the buttons:

This code should be placed in the KeyPad() constructor. It begins by instantiating the array itself. It then uses a for loop, bounded by the size of the array, to instantiate each individual button and insert it into the array. Note how the loop variable here, k , plays a dual role. It serves as the index into both the button array ( buttons ) and the array of strings that serves as the buttons’ labels ( labels ). In that way the labels are assigned to the appropriate buttons. Note also how each button is assigned an ActionListener and added to the panel:

An important design issue for our KeyPad object concerns how it will interact with the Converter that contains it. When the user clicks a keypad button, the key’s label has to be displayed in the Converter ’s text area. But because the text area is private to the converter, the KeyPad does not have direct access to it. To address this problem, we will use a Java interface to implement a . In this design, whenever a KeyPad button is pressed, the KeyPad object calls a method in the Converter that displays the key’s label in the text area.

Figure [fig-p493f1] provides a summary of the callback design. Note that the association between the Converter and the KeyPad is bi-directional. This means that each object has a reference to the other and can invoke the other’s public methods. This will be effected by having the Converter pass a reference to itself when it constructs the KeyPad :

Another important design issue is that the KeyPad needs to know the name of the callback method and the Converter needs to have an implementation of that method. This is a perfect job for an abstract interface:

The KeyPad can interact with any class that implements the KeyPadClient interface. Note that the KeyPad has a reference to the , which it will use to invoke the keypressCallback() method.

The implementation of KeyPad is shown in Figure 13.17. Note that its constructor takes a reference to a KeyPadClient and saves it in an instance variable. Its actionPerformed() method then passes the key’s label to the KeyPadClient ’s callback method.

Given the KeyPad design, we need to revise our design of the Converter class (Fig. [fig-p493f1] ). The Converter will now implement the KeyPadClient interface, which means it must provide an implementation of the keypressCallback() method:

Recall that whenever the KeyPad object calls the keypressCallback() method, it passes the label of the button that was pressed. The Converter object simply appends the key’s label to the input text field, just as if the user typed the key in the text field.

The complete implementation of this revised version of the interface is shown in Figure 13.18 on the next page. The appearance of the interface itself is shown in Figure 3.19.

Figure 3.19 shows that despite our efforts to group the keypad into a rectangular array, it doesn’t appear as a single entity in the interface itself, which indicates a layout problem. The default layout for our KeyPad (which is a JPanel ) is FlowLayout , which is not appropriate for a numeric keypad that needs to be arranged into a two-dimensional grid pattern, which is the kind of layout our design called for (Fig. [fig-metricgui2] ).

Fortunately, this flaw can easily be fixed by using an appropriate layout manager from the AWT. In the next version of the program, we employ the java.awt.GridLayout , which is perfectly suited for a two-dimensional keypad layout (Section 13.7.2).

The lesson to be learned from this example is that screen layout is an important element of an effective GUI. If not done well, it can undermine the GUI’s effort to guide the user toward the appointed tasks. If done poorly enough, it can even keep the user from doing the task at all.

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Part IX Case Studies

Part IX presents case studies that use a variety of Java EE technologies. This part contains the following chapters:

Chapter 51, Duke's Bookstore Case Study Example

Chapter 52, Duke's Tutoring Case Study Example

Chapter 53, Duke's Forest Case Study Example

Scripting on this page tracks web page traffic, but does not change the content in any way.

Java Arrays
Java Strings
Java Collection
Java 8 Tutorial
Java Multithreading
Java Exception Handling
Java Programs
Java Project
Java Collections Interview
Java Interview Questions
Spring Boot
Top 50 Java Project Ideas For Beginners & Advanced
Currency Converter
Brick Breaker Game
Attendance Management System
Number Guessing Game
Tic-Tac-Toe Game
Simple Banking Application
Library Management System
Word Counter
ATM Simulation System
Airline Reservation System
Smart City Project (City Guide Project)
A Text-Based Adventure Game
Grading System in Java
School Management System
Pharmacy Management System
Supermarket Billing System
Online Quiz Management System
HelpDesk Management System
Notes and Password Manager
Supply Chain Management System
Virtual Private Network (VPN) for an Office
Flappy Bird Game
Scientific Calculator in Java

Top 50 Java Project Ideas For Beginners & Advanced

Java is one of the most popular and widely used programming language and a platform that was developed by James Gosling in the year 1982. It is based on the concept of Object-oriented Programming. A platform is an environment in that develops and runs programs written in any programming language. Java is a high-level, object-oriented, secure, robust, platform-independent, multithreaded, and portable programming language.

Creating Java projects helps sharpen your skills and boosts your confidence as a developer. It provides practical application of theoretical knowledge. Building a portfolio showcasing completed projects empowers you for job interviews, giving you solutions, code, apps, and projects to display to recruiters.

With such amazing facts about Java, you would surely want to build some amazing applications using it, be it in any field like big data, mobile, enterprise, financial, or commerce. This article majorly focuses on projects which can be used by college students. Whether you’re from the first year, second year, third year, or fourth year.

In this article, you’ll learn about some amazing Java projects starting from beginner level, intermediate to advanced level. These projects can be utilized for college assignments and will assist you in developing your Java skill set.

Table of Contents Beginner Level Java Projects Intermediate Level Java Projects Advanced Level Java Projects

Beginner Level Java Projects Ideas

The below-given list consists of some beginner-level Java project ideas which can be used as major projects by the students or professionals.

1. Currency Converter

This project is a very basic project in Java that is used to convert a currency from one to another. A web-based interface for converting currency and getting the output value, for example, here displays converting the currency of the US dollar to INR.

Abstract: We see variations with different countries using different currencies. Be aware of the current exchange prices in the market and then can convert from one currency to another. A calculator-like application, developed using Ajax, Applet, and web features of Java servlets. You also get a regular update when there’s a change in the value of the country’s currency and also the conversion rate.

People use this application basically for business, shares, and finance-related areas where currency exchange and money transfer happen daily. You get a preferred choice to convert any country’s currency. Just enter the amount, the currency to which you want to transform to, click enter and you get the output.

Technologies Required: Java programming language, Java Servlets Web Features, Applet, and Ajax.

2. Brick Breaker Game

One of the pleasant ways to study technology is through implementing game applications. It may not be easy but developing this Java project will make you learn a lot of new things. This game development project will provide you with java experience and essential animation techniques with their integration.

Abstract: Many of you already heard of the brick breaker game. It has a small ball that knocks the bricks taking the help of a small platform at the base. The player handles this platform and tries to bounce the ball through that platform. In this project, the scoring depends on the number of bricked-broken, i.e., the more you destroy the bricks, the more you score.

If you missed the chance for the ball to bounce, then the game is over. This project is basically for beginners who are looking for a minor project. This simple project will surely help you with your first-year project or also as an implementation for fun purposes.

Technologies Required: Java, Game development, JFrame, JPanel, and Java Graphics Kit.

3. Attendance Management System

An attendance management system is one of the major projects for university-level graduates. The project can be built using Java, the MVC architecture could be followed, and Maven as a built tool. It uses MySQL as a backend for database management and uses a tomcat server to deploy the application in order to see it working live.

Abstract: This project is a web application that manages the attendance of any student in school or college, also employees in an organization. It has an admin feature that holds the access to do any kind of changes like update, delete, and add user records to the list.

Various users of the application where users can access are:

Technologies Required: Java Servlet , MVC architecture, Maven MySQL , Tomcat Server JSP, HTML , CSS , and JavaScript .

4. Number Guessing Game

This number guessing game is an easy project built on Java where the player has to guess a number given in between a range. If the guessed number is right, the player wins else, loses. It also has the concept of limited attempts where the player has to guess the number within the limited attempts given.

Abstract: The UI has an input value option where the player has to enter the guessed value, it also displays the time remaining to guess. After completing the limits given, if the guessed number is right, the player wins else loses. The range between the number can be from 1 to 100 or 1 to 1000. Also, if the number you’ve guessed is high or low to the actual value, the application sends you an alert “Too High” or “Too Low”. After the limited attempt is completed, the actual value is revealed.

Technologies Required: Java Programming Language and Random Class in Java .

5. Tic-Tac-Toe Game

The Tic-Tac-Toe game application is a simple project developed using GUI (Graphical User Interface) in Java. It is very easy to understand and play, players generally prefer this kind of game when they’re bored and want something to play which is quick and easy.

Abstract: The game starts with two players as active members, having a one-print board on the screen which displays 9 boxes (i.e., 3×3). The first person who starts the game has to enter either X or O for any one box, followed by the other player entering the other X or O (opposite to what the first player has entered). this continues unless any one of them gets a line cut either diagonally or straight. And the person who founds the line is the winner of the game.

Technologies Required: Java, Java Swing, Java GUI (Graphical User Interface), and JFrame.

6. Simple Banking Application

Simple Banking Application is a simple Java project for beginners to start their career in coding. You’ll learn about Scanner class to take inputs, and the basics of strings, loops, methods, and conditional statements. Here, simple banking operations like deposit, withdrawal, checking balance, exit, etc.

Abstract: In this modernized world, where time is money, everyone has got the habit of doing their tasks online. Within a click, a task is done. You get this application to make transactions just by sitting in your comfort zone. Every operation like money transfer and balance inquiry can be done in seconds.

Technologies Required: Java Programming Language, Oracle Database (if needed), and Java methods.

7. Library Management System

Learning Management System, this project build on Java is a great way to update the record, monitor and add books, search for the required ones, taking care of the issue date and return date. It comes with basic features like creating a new record and updating and deleting it.

Abstract: We rely on web-based applications for every task, be it small or big. This contains two sections – the admin and users section. The admin handles the record of the users and the user handles the entry of books being issued to him/her. Also, there can be modules that display the data of books available in the library, a search button to search for the required book, and the final payment method for the charges of the book or fine imposed.

Technologies Required: Java, Java Swing Library, MySQL JDBC Connector, MySQL Community Server, and rs2xml.jar (used to display the data in a table format).

8. Word Counter

A simple project for beginners is good to start. It can be built using Swing in Java. Here, the application tells you the no of words, the entered paragraph has.

Abstract: This Java application is best suited for counting words. Remember, our childhood days when we were asked to write an essay on a given topic where the word length should be 500 or 1000. This application comes with a feature that could help you. Along with word count, it also tells you the number of characters, words, and paragraphs it has. Also, it is completely free to use and there’s no word count limit.

Technologies Required: Java, Java Swing, Java Framework (JFrame), and Applet.

9. ATM Simulation System

ATM simulation system is a simple Java project for beginners. It is a kind of personal banking system where users can perform various transactions like withdrawals, deposits, and checking the balance of the account in just one click. It has a Graphical User Interface (GUI) to make the process user-friendly.

Abstract: The introduction of the application came up with two features which have an admin mode and the user mode. The admin mode is responsible for controlling the entire system like adding and deleting accounts and updating the records of the user. The user-mode takes care of the deposit, withdrawal, and checking of the account balance. The whole process of this system is automated, from PIN (Personal Identification Number) validation to the transaction. The card details will be secured enough by encrypting the details in the database and will only be accessible to the authorized user. The UI of the application contains a profile of the user, accounts added to it, and an option to withdraw, deposit and update details of the account.

Technologies Required: Java, J2EE, Apache Tomcat Web Server, and Oracle.

10. Airline Reservation System

This Java project is built to help the customers book tickets online, check the availability of seats, get the details of the flight arrival, select the class they want to choose, and departures reserve seats for national or international flights.

Abstract: This web-based Java project helps you in searching from pick-up location to destination, and filters out the flight details with timing, and available seats. It consolidates data from all airlines using globally distributed systems. After entering all the required details of the customer, it asks you to choose a flight with a preferred time slot, complete the payment, and book the ticket. It provides rates in real-time to customers as well as to travel agents. It also has two sections where you get to book a national and an international flight wherein you can book a domestic or international flight as per your choice.

Technologies Required: Core Java, HTML, JavaScript, and SQL Database.

11. Smart City Project (City Guide Project)

Smart City is a web-based application built using Java. It stores details of a city and displays information about the city such as hotels, shopping marts, restaurants, tourist places, transportation modes, and also some general info. This acts as a guide to the new visitors.

Abstract: Tourists and even general people travel from one place to another in order to explore or for employment purposes but before they explore, they want to get an insight data about the place. So, to help them with this, a simple city project can be the best guide for them. It is a web-based application written in Java which basically guides you about the place you’re going to visit. You can access all the details of the city. In this application, users need to sign up by entering input details and then can access all the required details of the city. It contains various modules like admin, tourism, business, and student wherein users can switch to the module as per the requirement.

Technologies Required: Java, JDBC ODBC 2.0 drivers, Oracle Database, J2EE, AJAX, and XML.

12. A Text-Based Adventure Game

A Text-Based Adventure game, built using Java and Data Structures is an interesting game where the player follows the commands given to him. This web-based gaming app is often referred to as interactive fiction.

Abstract: This game has a central character called the “Adventurer” which is like an object who represents the player. With the help of the object, tracking of the actual player can be made easy, also can find where the player is. The role of the adventurer is to type the commands which consist of one or two words. The commands which have to be followed can be Go, Look, Take, Drop, Use, and Exit. It contains the following classes TextAdventure, AdventureModel, Adventurer, and a number of rooms.

Technologies Required: Java programming language, Java objects and classes, and Array and Hashmaps.

13. Grading System in Java

This project built using Java is an important one to grade students based on their markings. It is the best project to start for beginners and has a GUI (Graphical User Interface) design.

Abstract: The main aim to build this project is to help schools and universities to manage the details of the students (like name, class, total subjects, marks achieved, etc) and rank them on the basis of marks. It manages the calculation of the average marks achieved and ranks the student on the basis of marks. It stores the data of students in a MySQL database. The project is built on Java and has a fully GUI (Graphical User Interface). It has all the features like managing the records of students, integrating all records of examinations, displaying all the information, and keeping a track of it.

Technologies Required: Java, Java Swing, MySQL Database, and JPanel.

14. School Management System

The School Management System is a Java application that stores records of schools be it related to students, teachers, and staff.

Abstract: This application’s objective is to help the school management system in managing the data easily. The manual system could be a complicated one when it comes to keeping the records so, there comes the role of this project. It holds personal records of students, teachers, and staff. This system contains modules for different roles be it admin, student, staff, and teacher. Here, the admin has to be responsible for maintaining the records in the database like adding users, updating the details of the user, and deleting the user’s profile.

Technologies Required: Java, MS Access database, Java Swing, Java Graphical User Interface (GUI), and JFrame.

15. Pharmacy Management System

Pharmacy Management System is a web-based application built using Java that offers you the facility to order medicines, consult doctors and keep track of all your orders online by just signing up with a registered mail id.

Abstract: This application is of great help to the users who regularly goes for body check-up because this application gives you the comfort of consulting with a doctor at your comfort place. It comes with an excellent and friendly user interface comes with an automated billing system. It has an integrated chat feature where you can consult with a doctor regarding your health and it also tells you details of medicines and you can also track the status of ordered items.

Technologies Required: Java, Java Swing, AWT, JDBC, and MySQL Database.

16. Supermarket Billing System

This web-based application is a Java project that is usually built for keeping the sales recording made on a daily basis. It uses a MySQL database for recording the data of the users, products, and orders made by the user (customer).

Abstract: The web-based Java application is implemented to keep a record of the products, status of the products orders, and user’s history. This UI is made in terms that it displays records of bills made on that particular day, items added to the new bill also have an automated system that calculates the bill with GST and other applied taxes and has a print button to print the copy statement of the bill. It has an admin module that is responsible for adding, updating, or deleting records of the bill. It maintains a database to store the items list, categories, and buyers list.

Technologies Required: Java, JDBC, MySQL Database, JSP, JavaScript, servlet, HTML and Ajax.

17. Online Quiz Management System

You must have definitely used this application during your school days when you were asked to attend an MCQ-based test. This Online Quiz Management System can be built using Java which contains different sections for questions, marks, and subjects.

Abstract: This Java-based project is online software that is a kind of an online platform for conducting mock tests and competitions. The UI is built in such a way that it displays the login button where the user has to sign in to begin the test, followed by entering the details of the test (which could be a unique key), then it displays the no of questions, time duration, and a “START” button to start the test. After completing the test, it asks you to review the answers and then submit it using the “SUBMIT” button. The admin module gives you access to the user’s profile.

Technologies Required: Java, J2EE, MySQL Database, and JDBC.

18. HelpDesk Management System

HelpDesk Management System built using Java, Servlet, and MySQL is a project made with the intention to help individuals raise a complaint regarding a ticket issued to them. It uses the MVC architecture design and Servlet can manage the request and response made.

Abstract: You face an issue, you raise a complaint, and a ticket ID is generated which can be used as a reference to resolve the issue. This application can be used in society, schools, organizations, and even in public places where people facing any kind of issues can register a complaint using the application. As soon you raise a complaint, a notification goes to the admin who verifies it and then reverts back to you after rectifying the issue. It includes features like Track, Issue, Ticket ID, Help Desk, Network, and Issues. It contains an admin and user module.

Technologies Required: Java, J2EE, HTML, JavaScript, MySQL database, Tomcat Server, JDBC, and Servlet.

19. Notes and Password Manager

This application is similar to a To-Do List app which helps you to complete your daily tasks and keep track of ongoing tasks. It also has a password for the users to log in to keep the data secure.

Abstract: This application is of great help when individuals have a lot of tasks to perform where some of them have to be done on priority. This application keeps a track of your daily tasks and helps you in completing them. This can be used by individuals and even by organizations to manage daily tasks. This saves their time as it stores their data in a centralized database for each user. The steps to follow are setting up the details, authenticating it with an authorized user, and managing notes and passwords. It comes with basic functionalities such as a login page, home page, note page, and updating details on the note page.

Technologies Required: Java, Android, XML, and Firebase.

20. Supply Chain Management System

Supply Chain Management System is a Java project for beginners where different operations such as inventory, storing, handling, and moving raw and finished goods to the final destination are completed.

Abstract: This project helps enterprises to move materials from source to destination. It is generally used by the production sector where sellers can add and update the details of the goods and the buyers can contact them regarding the booking of orders. Buyers can also check the availability of the goods and keep track of the status. It uses MS Access as a back-end, Apache Tomcat as a server, and HTML and CSS to design its front-end with Java. The main objective of this application is to avoid the communication gap between dealers and clients. There’s also a feedback feature for the goods received.

Technologies Required: Java, JDBC, JSP, HTML, and MS-Access Database

Intermediate Level Java Projects Ideas

The below-given list consists of some intermediate-level Java project ideas which can be used as major projects by the students or professionals.

21. Virtual Private Network (VPN) for an Office

Virtual Private Network (VPN) developed using Java can be your minor or major project. It works the same as WAN (Wide Area Network), and provides a private network across the public, for example, the Internet. A point-to-point virtual connection through traffic encryption, virtual tunneling protocols, or dedicated connections.

Abstract: This application built using Java provides a secure and private connection to the organizations. It can be used on office premises, as private networks and it can also be the best means to share information. This project also has three modules which are admin and marketing where the admin’s role is to handle the data stored of the members and the training module checks for the testing and networking part, and the marketing.

Technologies Required: Java, Java Servlet, J2EE, Apache Tomcat Server, HTML, and JavaScript.

22. Flappy Bird Game

Flappy bird game is a very simple Java-based gaming app in which the main character (which is the bird) has to reach the final destination after crossing all the hurdles. The use of the swing component in Java is perfect in this case.

Abstract: In this gaming application, the player has to control the movement of the bird. The fabby bird only ascends when there’s a tap by the player and descends the rest of the time. The count increase by 1 when the fabby bird passes one hurdle, also the time duration is counted. There shouldn’t be a collision with any hurdle, or else the game ends.

Technologies Required: Java, Java Swing, Java AWT, and OOPS.

23. Scientific Calculator in Java

A Scientific calculator built using Java is a general-purpose application whose primary objective is to perform basic mathematical operations and also perform some essential and tricky solutions to trigonometric functions, logarithms, etc.

Abstract: Here, Java Swing can be used to implement this project. It performs mathematical operations like addition, subtraction, multiplication, division, trigonometric operations, finding log values, etc. You get buttons to enter the input value and give the output within a second. In the program’s code, the use of switch cases can be seen to perform operations as per the case. The Scanner class can be used to take input from java.util package.

24. Simple Search Engine

You search for anything using a search engine so building a simple search engine can be one of the best projects. Applying a ranking algorithm can give better results.

Abstract: Simple Search Engine is a Java application developed using Servlets, SQL Server, and Oracle database. It can include features like a search bar, which displays the top 30 websites related to the keyword searched. The database containing resource description is described in SOIF (Summary Object Interchange Format) format. The interaction with the search server to access the database is dependent on the Java interface provided by classes in Java SDK. Your search engine contains a history of the pages you searched for, pages visited in the past few days, accounts linked with it, etc.

Technologies Required: Java, Java Servlet, Oracle or SQL Database, JDBC, Apache Tomcat, and JSP.

25. Online Voting System

An online Voting System built using JSP and Servlet can be the best project for college students. This project is designed to automate the voting process where multiple parties are added and then with the maximum votes, a leader is chosen.

Abstract: The main objective to build this web-based application is to reduce the time at the voting booth. The UI has different sections which display a login page to enter the portal, different parties with their symbol, an option to choose among them, and then to submit the entry. It uses HTML, CSS, and bootstrap in the front-end, MySQL is the database used, and also it uses an MVC design pattern. The user has to vote for the preferred party anonymously, but the voter’s information and total votes will be stored in the database.

Technologies Required: Java, JSP, HTML, CSS, MySQL, and Tomcat Apache Server.

26. Online Book Store

Online Book Store is an application that displays lists of books available in the store where you can purchase or even return them. You can check for the value of the book and buy it by sitting in your comfort place.

Abstract: The application created using Java allows users to purchase a book by checking for the availability of the book. The user has to sign up, check for the book, enter the credit card details, complete the payment and order the book. There are two modules in this application – the admin and the user. The admin is responsible for the entry of details and the user makes orders. Also, you can see the categories of the book such as Software, History, English, Science, etc. All the CRUD operations are performed by the admin.

Technologies Required: Java, HTML, CSS, JavaScript, Java Servlet, MySQL, and Tomcat server.

27. CGPA Calculator in Java

This CGPA Calculator built using Java is a web-based application that is of great help to university students. It can be built as a major project during your college days.

Abstract: This project can be built on eclipse using Maven and uses MVC architecture. It uses MySQL to store the data. This application creates a mark sheet for students and then calculates the CGPA. Here, also the admin is held responsible for entering the details, managing the user details, etc. In the UI, you can view a search key to enter the enrollment number and you get the details displayed in seconds. All the marks for the subjects are given semester-wise. When marks of all the subjects are entered, calculated CGPA will be auto-generated.

Technologies Required: Java, HTML, CSS, JavaScript, JSP, Java Servlet, MVC, Maven, MySQL, and Tomcat server.

28. Snake Game in Java

Remember, those days when you used to play the snake game on Nokia mobile phones. This snake game can be implemented fully using Java and uses a database using MySQL. It has all the functionalities with a full-featured Graphical User Interface (GUI).

Abstract: The application was built long years back and gained a lot of popularity within a few months. The game starts with a snake whose size increases with the no of apples eaten by it and the life of the snake ends when it gets collided with a wall or any kind of hurdle which comes in the way. So, basically, the more apple snake eats, the more score you get. The navigation is like a snake can turn left or right by ninety degrees. A constructor can be used to start the movement of a snake and a function to perform various other operations.

Technologies Required: Java, MySQL Database, JDBC, Java AWT, J-Frame, and Java Swing.

29. Job Portal in Java

One thing which comes to your mind when you complete your graduation is getting a job. So, building a job portal for individuals where after entering the qualifications, the user gets the opportunity to enroll himself/herself for the job preferred.

Abstract: The main objective of the online job portal project in java is to make the right job available for the right candidate. The admin, the recruiter, and the user are the three most vital parts of this application. Here, as soon as you enter the details or qualifications pursued by you, the recruiter verifies it and takes the further procedure ahead. The process includes verifying the details, contacting the concerned person, having all the interviews done, and receiving an offer letter. The database (which can be MongoDB) stores the data of the user. The user performs CRUD operations and deletes the profile as soon as the user gets a job.

Technologies Required: Java, HTML, CSS, JavaScript, JSP, Java Servlet, MySQL Database, and Tomcat server.

30. Online Cab Booking System

Ola and Uber are the online cab booking system that almost every one of us has become used. So building such a Java application would be the best idea.

Abstract: In this project, the main objective is to help customers in booking a cab to reach their destination with pick-up as their preferred location. The application fetches your pick-up location and asks you to enter the drop location, when entered, finds a cab driver nearby and even tells you the calculated time the cab will take to drop you at the location. The system is designed using Spring MVC, Servlets, Hibernate, JDBC, JSP, HTML, and CSS.

Technologies Required: Java, HTML, CSS, JavaScript, JSP, JDBC, Java Spring, Java Servlet, MySQL, and Tomcat Server.

31. Crime Records Management System

Based on the number of crimes being committed, this crime record management system is a secured application built using Java. It allows you to keep a record of the entries made of the number of crimes being committed.

Abstract: This Java-based web application runs on a Tomcat server and uses MySQL as a database. Its main features include managing crimes, Handling FIRs, records of criminals, and complaints registered. You can develop a secured application using EJB, Spring, and Hibernate. You need MySQL database to run this project and MySQL J-Connector to make connections between MySQL and Java.

Technologies Required: Java, JSP, JDBC, MySQL, and Tomcat Server.

32. Color Hunt Gaming Project

This Java-based gaming application is a mind game consisting of differently-colored letters which are randomly arranged. It is a kind of mind game that is built with the intention to increase your thought process.

Abstract: Basically, in this game, there are different colors printed on the text, whatever statement gets displayed, you have to click on the mentioned color. As soon as you click on one, the other comes suddenly. You lose points when you don’t click on the color displayed. There’s also a time limit given in which you have to reach a given number of points. This game is built in such a way that it can only be played on android phones.

Technologies Required: Java, Android, and XML.

33. Online CV/Resume Builder

You’re ready to apply for a job but don’t have an interesting CV/which perfectly shows your skills and qualifications. Online CV/Resume Builder comes to the rescue where just by entering required details you’ll get your CV/Resume in pdf format which is auto-generated.

An online resume builder project is an internet-based application that can help students and other professionals to get an instant resume template, which they can fill easily with their credentials. An online resume builder provides different standard templates that can be downloaded in different formats like PDF and others. A user will not have to spend a lot of time on formatting and designing his or her resume. He will only enter his particulars and download his CV on the go.

Abstract: The online resume/cv builder application helps job seekers to build a CV with a proper format. It has different templates to choose from wherein you can opt for the best one. This application contains various modules which are user, skills, job, salary, and resume. Using these modules, different sections of a CV are made and after entering the details you get a properly organized CV.

Technologies Required: Java, MySQL Database, JDBC, Java Servlet, JSP, and Tomcat Server.

34. Weather Information System

This application tells you the weather-related information about your location and also of other locations. This Java-based application can be the best project for your minor project submission.

Abstract: Due to the change in weather, we can predict whether it’s going to be a rainy day, sunny day, or cold day. But sometimes, all of a sudden you see climate change. With the help of a weather information system which is a Java-based project, you can get to know the temperature not only your but also worldwide. The application picks up the default location and displays the weather data report. It tells you the temperature, rain, humidity, and even the direction of the wind blowing.

Technologies Required: Java, Java Servlet, J2EE, Tomcat Server, HTML, CSS, and JavaScript.

35. Exam Seating Arrangement System

Exam Seating Arrangement System, the application implemented using JSP, Java, and MySQL. This application will help the examination handling manager to organize the allocation of seats for all the students.

Abstract: This application takes in the details of the students be it name, roll no, section, branch, or year and stores it in databases. The admin is held responsible for managing the details, here the application is made to automate the seats allocates to students and this final list goes out on the day of examination which helps in not getting the seats revealed prior. The modules existing here are the student module, admin module, and seat module. This automated system helps in maintaining the record and proper functioning of the system.

Technologies Required: Java, HTML, CSS, JSP, JavaScript, MySQL, and Tomcat Server.

36. Traffic Controller System

The Traffic Controller System is a Java JSP and MySQL-based project, which is developed for process automation of the Traffic Controller System.

Abstract: The objective of this application is to create a system that controls the traffic which is done by implementing a set of classes and interfaces. The main features can be traffic lights, routes, diversions, and traffic police. It is a secured application that runs in the JVM. A GUI is created using JavaFX and classes for performing different operations such as the structure of the traffic network, and the main view of the system. The simulation is carried out to handle input and events that are being executed.

37. Disaster Management System

Disaster Management System is a Java-based application that identifies and implements techniques for reducing the causes of the disaster and the losses faced. It can be the best project to avoid natural disasters.

Abstract: Applications like this have four stages: mitigation, readiness, response, and recovery. Each process aims to reduce the risks occurred due to natural disasters like earthquakes, tsunamis, etc. The process follows when there’s a report submitted by the affected region, the data is collected and reported to the concerned authority to take measures. It is a web-based Java Swing project which stores data in MySQL for future references. The UI can have a login page, lists of earthquakes that happened, a new user page, and a user list.

Memory Game – Flipping Tiles

Technologies Required: Java, Java Swing, JSP, JDBC, MySQL, and Java Servlet.

38. I-D Card Generator System

ID Card Generator System is a web-based Java project which uses the Swing library. It generates an ID of the entered details of the individuals and gives you a copy of it.

Abstract: Application like this can be used in schools and offices where you require an ID card to enter the premises. In this project, you just need to log in and enter your personal details like name, age, blood group, designation, and the joining date, when you enter the required details, you get a copy of the ID card. The features can be storing the data in the database, having a unique identification number assigned to each individual, and no forgery allowed.

Technologies Required: Java, Java Servlet, Java Swing, JSP, HTML, CSS, JavaScript, JDBC, MySQL, and Tomcat Server.

39. Memory Game – Flipping Tiles

Memory Game is a mind game where you have to remember the position of tiles placed earlier and re-assign them within the stipulated time. This game is implemented to play with your mind and bring the best.

Abstract: This Java-based gaming application is built using Swing. This game’s intention is to test our memory, here, we see an even number of tiles in which each number has a pair. All the tiles are kept facing downwards, all the tiles have to be flipped one by one, and when two tiles get matched they are removed from the tile. When there’s no match, the tiles are kept back in position.

Technologies Required: Java, Java Swing, Java OOPS, and ArrayLists in Java.

40. Chat Application

Chat application has gained great popularity among individuals these days. This is similar to Instagram, Facebook, and Orkut.

Abstract: This online chat application using Java uses graphical components in the Swing toolkit in Java and uses MySQL as a database. Its features include signing up, signing in, chatting, sending and accepting requests, and creating groups. You can also create a free account. It also checks whether there’s any fake account and gives no access to the user.

Technologies Required: Java, Java Swing toolkit, MySQL, Java AWT, and JDBC.

Advanced Level Java Projects Ideas

The below-given list consists of some advanced-level Java project ideas which can be used as major projects by the students or professionals.

41. Social Networking Site

Social Networking Site has gained a lot of popularity among individuals. It is Java JSP and MySQL project, running on the tomcat server. The management of users, photos, and videos are taken care of by this system.

Abstract: The application has many features including a login page, a home page displaying all the posts by friends added to your account, a notification page displaying all the alerts, and a profile page where you can edit the details, and also upload a picture of yours. It uses HTTP requests to complete the operation which is being sent to the server. The process that the server follows is decoding the request, authenticating the user, and making changes to the database. JSON is used here to encode the result if found anything other than boolean.

Technologies Required: Java, Maven, J2EE, HTML, CSS, Java Servlet, JDBC, MySQL, and Tomcat Server.

42. Bug Tracking System

A system that keeps track of bugs that occurred during the development of a project. This Java-based application is created to help developers to manage bugs/errors occurring during SDLC.

Abstract: Bug Tracking System is an application that focuses majorly on tracking the bug and changing its status. When the developer gets the help of a bug tracking system, he/she gets an assistant to help him/her during SDLC. The modules present in this can be the developer, admin, and management modules. The system records all the bugs in their detail so that the developer can work on them one by one.

Technologies Required: Java, JDBC, JNDI, Servlets, JSP, Oracle/Access, RetHat JBoss AS, JavaScript, HTML, and CSS.

43. Text Editor in Java

Text Editor built using Java is similar to a notepad application. You can also create text documents and the system gives you the feature to edit the text entered in it.

Abstract: A Text Editor built using Java uses JTextArea, JMenu, JMenuItems, and JMenuBar to perform various tasks. It allows the user to enter, change, store, and print text. It also has a file menu to make changes in files (like open, save, close, and print) for future references. and an edit menu to cut, copy and paste texts. Also, it has a “Save and Submit” button to close the file after saving the data. An actionListener is also used to detect actions in the project.

Technologies Required: Java, Java Swing, Java AWT, JTextArea, JMenuBar, JMenu, and JMenuItems.

44. Digital Steganography

Security is a major concern be it in organizations, military, hospitals, schools, etc where data plays an important role. Keeping the data secure is much needed and here is a Java-based project for advanced programmers which is digital steganography.

Abstract: Digital Steganography is the process in which data is sent from one point to another without affecting other users and also keeps the data secure. It uses multimedia as a covering medium. It embeds the text or image and stores it in the least significant bits of the image. It doesn’t even create suspense for the hackers. This is the best project advanced programmers on Java can work on. It contains both sender and receiver side programs to let the user choose whether to send or receive data.

Technologies Required: Java, Java Servlet, MySQL or Oracle Database, JDBC, TomCat Server, JSP, HTML, CSS, and JavaScript.

45. Criminal Face Detection System

The Criminal Face Detection System application is built to detect the faces of criminals by matching them with the pre-existing data in the database. Although, there are so many ways to identify a criminal this could be the best way, and also building this project for advanced programmers is easy.

Abstract: The project is intended to use the images previously taken and identification will be done according to images taken of different people. This project aims to build an automated CFD system by levering the human ability to recall minute details in the facia. The criminal Face Detection System project aims to build a Criminal Face Detection system by levering the human ability to recall minute facial details. Identification of criminals at the scene of a crime can be achieved in many ways like fingerprinting, DNA matching, or eyewitness accounts. Out of these methods, eyewitness accounts are preferred because it stands scrutiny in court and it is a cost-effective method. It is possible that witnesses to a crime have seen the criminal though in most cases it may not be possible to completely see the face of the perpetrator.

Tip: We can also get this project done in Python language even better because of help of existing present libraries out there namely numpy and other tools: Keras. It will be easier to do in python language but doing via java makes one crystal clear about networking, machine mearning and java aplllciation onboard running concepts clear.

Technologies Required: TensorFlow, Core java, Machine learning, SQlite, OpenCV(eccentric tool), Strong knowledge of advanced java concepts.

Criminal Face Detection System Java Project

46. Airline Reservation System with Advanced Features

With the increase in modernization, everything has come online. This application helps customers book flight tickets by just being at their comfort place and also searching for the availability, and timing of the flight.

Abstract: To ease and automate the registration process system provides information like passengers information and a criminal list of all passengers. The software consists of 4 modules: User registration, login, reservation, and cancelation. The project includes online transaction fares, inventory, and e-ticket operations. Do remember not to mix it with Library Management System as here we have to go to and perform something where here it is a process. Yes, it seems easy on the skills side as mentioned below which are required.

Prerequisites Required: By far we are aware of Applets, Servers, Servlets, AWT, and Core Java concepts already with Collection Framework.

Technologies Required- Core Java, Java Swing, Java AWT, Java Applet, Database-MySQL

47. Advanced Chatting Application

When everything has come online, chatting is also performed online be it your online friends or anyone. Hence, this advanced chatting application has advanced features like smooth communication with video and audio call facilities, and many more.

Abstract: There is not only one system rather we dop have multiple systems connected together. Client and Server communication takes place instead of basic request-based communication. This application will need to communicate through Sockets . The server and client can run on different computers in the same network. There can be multiple clients connected to a server and they can chat with each other. These days with every application, we are having a feature ‘Help’ to chat with a bot right from traveling apps such as Ola, and Uber to food apps such as Zomato, and Swiggy, this chatbox is embedded in every.

Sockets are something new that one has to learn here in adhering to the advancement of the project because they will be used for networking, and TCP/IP protocols so communication can be built.

Technologies Required: Core Java, Java Network-based libraries, Java Sockets, File handling, and Exception Handling.

48. Customer-Relationship Manager

It is a bit tedious but an easy pick among advanced-level java projects. It is also one of the most important projects as CRN is used by nearly all organizations, institutions,s or any software company as well to keep updated with the records. Do not confuse it with working just with awt and core java, as here we need to fetch it over a larger dataset in real-time for which we need to inculcate tools like Hibernate, MVC, CSS, JDBC, etc. Do create in a high-tech way invoking the above tools so that internal working of such tools can be perceived.

Abstract: It is the easiest of all projects at the advanced level as the name suggests that we have to build an application where we will be building relationships with customers by adding new customers in software, editing, and deleting the info whenever needed. The customer relations manager will keep track of all the customers. Adding new customers, editing their information, and deleting them when needed. Fetching already recorded customer details whenever required.

Technologies Required: Spring Framework, Hibernate, HTML, CSS, JDBC, CRUD, MVC, and DB(MySQL)

49. Email System

A great medium to conversate in an official way is through e-mails. Email system implemented using Java is of great value to organizations. So, advanced programmers can focus on the implementation of this project

The project functions something like this – the ISP’s (Internet Service Provider) mail server handles the emails sent from an ISP. All the sent emails first come to the mail server, after which they are processed and forwarded to the collector’s destination where another mail server is located.

The mail server on the collector side receives the incoming emails and sorts them electronically in the inbox. Now, the recipient can use their email application to view the received emails. The entire transaction occurs by directly connecting to the mail server through the program, which makes it much safer than the existing email client software.

Abstract: This Email System is designed for sending and receiving emails for official communication which has a proper format. This system can use HTTP port 80 to access emails, also the two main protocols which can be used are SMTP (Simple Mail Transfer Protocol) and POP3. Java mail API can be used to transfer data. The ISP mail server receives all the mail sent, processes it, and then forwards it to the destined address.

It is one of good project ideas among advance level project as it is of hard nut among projects we have discussed above and it will take a lot of time to properly build it.

Technologies Required: Event Handler, HTTP, Protocols (like SMTP and POP3),

50. Advance Sudoku Game

Sudoku Game is something which almost every one of us must have played. This game is all related to logic-building so once you play this, it gets easy for you to build logic so building this application is of great use.

Abstract: Building the same common sudoku game but with help of JavaFX. Generating a new game from a solution, keeping track of user input. Checking user input against the generated solution. Keeping track of selected numbers will be necessary for some of the functions and also the ability to check for errors and give hints in which we can invoke trained models from larger datasets from machine learning and artificial intelligence.

Technologies Required: Core Java , Java FX , Event Listeners , MVC, Collection API

FAQs on Java Projects

Q.1 why use java.

Java is simple to learn programming language because doesn’t contain concepts like : Pointers and operator overloading and it is secure and portable.

Q.2 What is the difference between C++ and Java?

C++ JAVA C++ is platform dependent. Java is platform-independent. C++ uses a compiler only. Java uses a compiler and interpreter both. C++ support pointers and operator overloading. Java doesn’t support pointers and operator overloading concepts. C++ does not support the multithreading concept. Java supports the multithreading concept.

Q3: What are some good Java projects for beginners?

Here are the top 5 Java projects for beginners: Simple Calculator : Create a basic calculator application that performs arithmetic operations such as addition, subtraction, multiplication, and division. Address Book : Build an address book application that allows users to add, view, update, and delete contact information. Tic-Tac-Toe Game : Develop a simple console-based tic-tac-toe game where two players can take turns marking their moves on a grid. Hangman Game : Implement a text-based hangman game where players guess letters to reveal a hidden word. Temperature Converter: Design a program that converts temperatures between Fahrenheit, Celsius, and Kelvin scales. These projects are beginner-friendly and provide a solid foundation in Java programming concepts.

Q4: What kind of projects is Java used for?

Java is used for a wide range of projects, including web development, Android app development, enterprise software, big data processing, scientific computing, and financial applications.

Q5: Is Java worth learning in 2023?

Yes, learning Java in 2023 is highly beneficial due to its wide usage in enterprise applications, Android development, and strong community support. Java remains a valuable skill with abundant job opportunities and a versatile ecosystem.

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Chapter 1 - Case Study

Case study based questions from revision of class ix syllabus, class 10 - apc understanding computer applications with bluej, case study based questions.

Generally, a computer language uses either compiler or interpreter (a set of programs) to convert source code into object code. But Java, a case sensitive language, uses both the translators (i.e., compiler as well as interpreter). Firstly, compiler converts the Java source code into an intermediate code which is further converted into machine code with the help of an interpreter.

Based on the above discussion, answer the following questions:

(a) Which of the following statement is true?

Java compiler is a hardware.
Java compiler is a software but interpreter is a hardware.
Both the translators are hardware.
Both the translators are software.

(b) The intermediate code is referred to as:

Assembly code

Artificial machine
Virtual machine
Real machine
Normal machine

(d) What is meant by a case sensitive language?

It understands only lowercase letters.
It understands only uppercase letters.
It distinguishes between lowercase and uppercase letters.
It doesn't distinguish between lowercase and uppercase letters.

(a) Both the translators are software.

(b) Byte code

(d) It distinguishes between lowercase and uppercase letters.

An operator is basically a symbol which performs arithmetical and logical operations to yield meaningful results. There are three types of operators used to perform any operation in Java programming. They are arithmetical, relational and logical operators. The arithmetical operators are used to perform arithmetical calculations. They are unary, binary and ternary operators. The syntax of using ternary operator is:

(a) A/An ............... operator works on a single operand.

(b) Which of the following is not a logical operator?

switch-case

(d) Which of the following is a relational operator?

Functions are the built-in modules that can be used in our program to perform a specific operation. There are some mathematical functions that are used for specific functions. For example, we can use Math.sqrt( ) function to return square root of a positive number, Math.random( ) and Math.ceil( ) to return random number in a range of numbers to return the next higher integer number.

(a) What will be displayed, if the following statement is executed? System.out.println(Math.sqrt(-25));

Logical error

(b) Math.random( ) function returns a random number in the range:

between 0 and 1
between -1 to 0
between -1 to 1
None of the above

Math.max( )
Math.min( )
Math.floor( )
Math.ceil( )

(d) Which of the following statement is true for Math.max( )?

It will always result in int type value.
It will always result in double type value.
The resultant data type will depend upon the type of arguments.
It will return float type, if arguments are double type.

(b) between 0 and 1

(d) The resultant data type will depend upon the type of arguments.

Java, like all other programming languages uses some statements that allow us to check a condition and execute certain parts of a code depending on whether the condition is true or false. Such statements are called conditional statements. We can also use a conditional statement within another conditional statement. The inner conditional statement is executed only when the outer condition is true. The conditional statement can also be a multiple branching statement.

(a) Which of the following is not a decision making statement?

(b) A conditional statement used within another conditional statement is known as ...............

nested conditional statement
embedded conditional statement
accumulated conditional statement

if and only if

(d) Which of the following is not a component of multiple branching statement?

(b) nested conditional statement

The following program segment calculates the norm of a number. The norm of a number is the square root of sum of squares of all the digits of the number. Sample Input: 68 Sample Output: The norm of 68 is 10 [Hint: 6x6 + 8x8 = 36 + 64 = 100 The square root of 100 is 10. Hence, norm of 68 is 10] There are some places in the program left blank marked with ?1?, ?2?, ?3? and ?4? to be filled with variable/function/expression.

(a) Which of the following will be filled in place of ?1?

in.nextInteger;
in.NextInt( );
in.nextInt( );
in.nextint( );

(b) What will you fill in place of ?2?

(d) What will you fill in place of ?4?

Math.sqrt(s)
Math.SQRT(s)
Math.sqrt(n)
Math.sqrt(num)

(a) in.nextInt( );

(b) num > 0

(d) Math.sqrt(s)

The completed program is given below for reference:

Software Developers
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