Java Interview Questions with Answers

1. Top Java Interview Questions with Answers Introduction If you want to prepare for a Java interview, you have come to the right place. If you are a beginner and want to upgrade your skills, it is important to understand the most commonly asked Java interview questions. JAVA is the language that is widely used for programming in the world, and interviewers mostly focus on both basic and core concepts to check your knowledge. We have put together some of the most common Java interview questionsand answers to help you feel prepared and confident for your interview. In this article, we cover everything from variables and loops to oops the concept, making it the best starting point for fresher’s and experienced developers. Q1. What is JAVA? Sun Microsystems created Java as a programming language. It's easy to use and based on objects. The great thing about Java is that you can run the same program on any device with a JVM, without changing the code. JAVA is secure, fast, and powerful. It is used to develop: Mobile Apps Desktop Apps Games Database connection and more. Web Apps

2. Q2. What are JDK, JVM and JRE? JDK: To develop Java applications, programmers use the JDK (Java Development Kit), which includes all the necessary tools. JRE: To run Java programs, you need the JRE, which is the tool that lets your computer understand and run Java code. It includes JVM and core libraries. JVM: JAVA Virtual Machine is used for executing JAVA bytecode. It is part of JRE. Q3. Features of JAVA? JAVA’s main features include: Platform-independent Object-oriented Secure Multithreaded Robust High performance Q4. Can you name the four key principles of object-oriented programming in Java? Encapsulation Polymorphism Abstraction Inheritance Q5. What is the difference between C++ and JAVA? C++ JAVA It is platform-dependent There are pointers in C++ Do not have Garbage Collection Does not support multithreading JAVA is platform-independent There are no pointers in JAVA Have Garbage Collection JAVA supports multithreading Q6. What is Bytecode?

3. When a JAVA compiler compiles a class, it generates a .class file, which is called Bytecode. It contains a set of instructions. Bytecode is a special kind of code that can run on any machine because it works through the JVM. Q7. Explain the ‘final’ keyword. The final keyword is used in Java (and some other programming languages) to indicate that something cannot be changed or overridden. Q8. Types of classloaders in JAVA. Three types of classloaders in JAVA are: Bootstrap classloader (loads rt.jar file). Extension ClassLoader: This loads all the JAR files found in the extension folder.  System ClassLoader: loads .class files from the paths set in the classpath.. Q9. What is JIT compiler? It stands for Just-In-Time. The JIT (Just-In-Time) compiler converts bytecode into machine code while the program is running, helping it run faster. By this, the overall performance of the JAVA apps is optimised. Q10. What is a default package in JAVA? In Java, java. lang package is imported by default in all the classes of Java. Also, no- name package (also called default package). Q11. How many memories are there in JAVA? We have five memories in JAVA: Heap Method area PC register JAVA stack Native method stack Q12. What does the .class file contain? A .class file contains bytecode instructions.

4. Q13. What is data encapsulation? Encapsulation is an OOP principle where variables and methods are bundled together into a single unit (class). It controls who can see or change the data by using access modifiers like public and private. Q14. Explain the main method in Java Syntax: public static void main(String[] args) Public–The method must be accessible from anywhere so that the JVM can call it. static –JVM wants to call this method without using an object reference. void – The main method doesn’t send any value back to the JVM when it finishes. main –The name given to the method where the program starts running. String [] args –Itis used to get input from the command line when you run a program. Q15. What is function overloading? It lets you create several methods with the same name, as long as they take different kinds of input. The compiler differentiates them based on the number of parameters. Q16. What is function overriding? It lets a subclass give its own version of a method that it inherits from its parent class. It enables runtime polymorphism. Q17. Types of blocks in JAVA? Static block Instance block Local block Q18. What is a final class? In Java, a final class is a class that cannot be extended (inherited) by any other class. It is declared using the final keyword. Syntax: final class Vehicle {

5. // class body } Q19. What is Abstraction? Hiding the complex implementation and showing an important feature is called abstraction. Q20. What is inheritance? It is a mechanism where a child class inherits the properties and behaviour of a parent class. Achieved using the extend keyword. Allow method overriding for polymorphism. You use super to get things from the parent class, like methods or variables. Supports single and multilevel inheritance. Q21. What is polymorphism? Polymorphism in Java is the ability of an object to take many forms. It allows a single interface or method to operate on different types or perform different behaviors. Compile-time polymorphism: Polymorphism that happens during compile time. Run-time polymorphism: Achieved by method overriding. Q22. What is an interface? An interface in Java is a blueprint for a class. It is a collection of abstract methods (method signatures without a body) that define what a class must do, but not how it does it. Q 23. When to use an interface? Interface can be used in Java when you want to define a contract that multiple classes can follow, regardless of how they implement the behaviour. Also, this will make classes more modular and structured. Q 24. What does the JAVA compiler do? Syntax verification Verify the compatibility issues. Will convert source code into bytecode.

6. Q 25. What is bytecode and bitcode? The operating system understands bitcode directly, but bytecode is designed to be understood and executed by the JVM (Java Virtual Machine). Q 26. What are the literals in JAVA? A literal is a fixed value that you directly assign to a variable, like a number, character, or string. In Java, we have five types of literals: Integral literal Floating point literal Boolean literal Character literal String literal Q27. What is a POJO class and a JAVA bean class? POJO class: A class is said to be a POJO class if it supports the following two properties: All variables must be private. Every variable should have a setter to update its value and a getter to read its value. Bean class: A class is said to be a JAVA bean class if it supports the following four properties: A class must be public. A class must have a constructor. All variables should be private. All variables should have a setter and a getter method. Q28. What is a constructor in JAVA? When a method has the same name as the class and doesn’t have a return type, it is called a constructor. it’s a unique function designed to set up an object when it is created. Having the same name as the class name.

7. It will execute when we create an object. Does not allow any return type. Q 29. Explain the types of constructors In Java, a constructor is a special method used to initialize objects. It is called automatically when an object is created. He two types of constructor are as follows: 1)User-defined Constructor: A constructor that is created by the user based on the application requirement. It is categorised into two types: Zero-argument constructor: When we are not passing any argument to a user-defined constructor, it is a zero-argument constructor. Parameterised constructor: When we pass at least one argument to the user- defined constructor, then it is called a parameterised constructor. 2)Default Constructor: If you do not put any constructors in your class, the JAVA compiler inserts a default constructor into your code. A default constructor is an empty implementation. Q 30. What is constructor overloading? Having the same constructor name with different parameters in a single class is called constructor overloading. Q 31. What is method overloading? It allows you to use the same method name for different tasks by changing the number or type of parameters. All the methods present in a single class are called overloaded methods. Method resolution will be taken care of by the compiler based on reference type. Example: Class Z { Public void n1 () { System. out. print (“0 argument method”) } Public void n1(int j) {

8. System. out. print (“1 argument method”) } } Q 32. What is method overriding? Writing two or more non-static methods in a super and subclass in such a way that the method name, along with the method parameter, must be the same is called Method overriding. Example: class D { public vod s1() { System. out. print (“Deep”) } } Class E extends D { public void s1() { System. out. print(“t point tech”) } } Q 33. Explain this keyword. A “this” keyword in JAVA is used to refer to the current class object reference. We can utilise this keyword in the following ways: To refer current class variable. To refer current class method. To refer current class constructor.

9. Q 34. What is a super keyword? A “super” keyword in JAVA is used to refer super class object. We can utilise this keyword in the following ways: To refer to a superclass variable. To refer superclass method. To refer to the superclass constructor. Q 35. What is an API? API stands for application programming interface. It provides developers with the essential tools and resources to create software applications. API is a collection of packages. We have three types of API: 1.Pre-defined API: A built-in API is known as a predefined API. 2.User-defined API: An API, which is created by the user based on the requirement, is called a user-defined API. 3.Third-party API: API that a third-party vendor provides. Q 36. What is the sealed keyword in JAVA? It is one kind of restriction that describes which classes and interfaces can be extended or implemented from a sealed class or interface. Q 37. Define the instanceof operator? The instanceof operator in Java is used to test whether a reference variable is associated with an object of a specific class or interface. Q 38. What is a package? A Package is a collection of classes, interfaces, enums, annotations, exceptions and Errors. Enums, Exceptions and Errors are a special class, and Annotation is a special interface. A package is also known as a folder or a directory. Q 39. What is an Array? A regular variable can store just one value at a time. To store more than one value in a single variable then we use an array.

10. An array is a data structure that holds multiple items of the same type, stored together in a sequence. Q 40. What is recursion? A method that is called by itself many times is called recursion. Recursion is similar to looping. In recursion, post-increment and post-decrement are used. Q 41. What is Enum? An enum is a group of named constants. The Enum concept was introduced in version 1.5. Using an enum, we can create our own datatype called an enumerated datatype. Java enums are more powerful as compared to another language's enum, Syntax: enum enum_type_name { Value1,vaue2…..value n } Q 42. What do you mean by a functional interface in Java? A functional interface is a special type of interface in Java that defines only one abstract method. It’s mainly used for implementing lambda expressions. A functional interface can be annotated by @Functional interface annotation. Q 43. What is lambda expression? A lambda expression in Java is a short block of code that takes in parameters and returns a value. It is used to concise our code more well, and help to remove boilerplate code. Q 44. What is the type parameter<T> in JAVA? It is a technique through which we make our application independent of the data type. It is represented by <T>. Q 45. Explain exception handling.

11. Exception Handling in Java is a mechanism to handle runtime errors through which the normal flow of the application can be maintained. It is an unexpected situation in a normal execution flow. An exception was encountered due to the following reasons. • The user gave the wrong input. • part to complete the task, then there may be a chance of getting an exception. Due to dependency, when one part of the program is dependent on another Q 46. Different criteria of Exception? i) java.lang.ArithmaticException ii) java.lang.ArrayIndexOutOfBoundsException iii) java.lang.StringIndexOutOfBoundsException iv) java.lang.NegativeSizeArrayException v) java.lang.NullPointerException vi) java.lang.NumberFormatException vii) java.util.InputMismatchException Q 47. When to Use try, catch, and finally Blocks in Java? The try-catch-finally construct in Java is used for exception handling—it allows you to catch errors, handle them gracefully, and execute cleanup code reliably. Whenever our statements are error-suspecting or risky, we should write the Statement inside the try block. If something goes wrong while the code inside the try block is running, the catch block takes care of the error so the program can run smoothly. The catch block only runs when there's an exception. The finally block always runs in the end, no matter if an exception was thrown or everything runs smoothly.

12. Conclusion: Understanding the top Java interview questions and their answers is essential for anyone aiming to build or advance a career in Java development. These questions cover the core fundamentals (like OOP, constructors, interfaces, and exception handling), advanced topics as well. By studying these questions, you will boost your confidence. Although there are many websites to provide Java interview questions but, I suggest you go to Tpoint Tech website that offers Top Java Interview Questions with Answers. It also provides you with an online Java compiler through which you can run your Java code in an easier way.