Java Frequently Asked Interview Questions & Answers

List of  20 FAQ & Answers (Java Interview): 

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1. What is Java?

2. What is the difference between JDK, JRE, and JVM?

3. What is OOP?

4. What are the pillars of OOP?

5. What is the difference between abstract class and interface?

6. What is a constructor in Java?

7. What is method overloading and method overriding?

8. What is encapsulation?

9. What is inheritance in Java?

10. What is the final keyword in Java?

11. What is a static method in Java?

12. What is a static variable in Java?

13. What is a package in Java?

14. What is a thread in Java?

15. What is synchronization in Java?

16. What is the difference between ArrayList and LinkedList?

17. What is a HashMap in Java?

18. What is an exception in Java?

19. What is a try-catch block in Java?

20. What is a finally block in Java?

Question 1. What is Java?

Answer: 

Java is a high-level, object-oriented programming language developed by Sun Microsystems (now owned by Oracle Corporation). It is designed to be platform-independent, allowing programs to run on any device or operating system that has a Java Virtual Machine (JVM) installed.

Question 2. What is the difference between JDK, JRE, and JVM?

Answer:

JDK (Java Development Kit) is a software development environment used for developing Java applications. JRE (Java Runtime Environment) is the environment required to run Java programs. JVM (Java Virtual Machine) is a platform-independent execution environment that converts Java bytecode into machine code.

Question 3. What is OOP?

Answer:

OOP (Object-Oriented Programming) is a programming paradigm that uses objects and classes to represent and manipulate data.

Question 4. What are the pillars of OOP?

Answer:

The pillars of OOP are: encapsulation, inheritance, and polymorphism.

Question 5. What is the difference between abstract class and interface?

Answer:

An abstract class is a class that cannot be instantiated and is used as a base class for other classes. An interface is a collection of abstract methods that can be implemented by any class.

Question 6. What is a constructor in Java?

Answer:

A constructor is a special method that is used to initialize objects of a class. It has the same name as the class and is called automatically when an object is created.

Question 7. What is method overloading and method overriding?

Answer:

Method overloading is the ability to have multiple methods with the same name in a class, but with different parameters. Method overriding is the ability to define a method in a subclass that has the same name and signature as a method in the superclass.

Question 8. What is encapsulation?

Answer:

Encapsulation is the practice of hiding the internal details of an object and exposing only the necessary information to the outside world.

Question 9. What is inheritance in Java?

Answer:

Inheritance in Java is the mechanism by which a new class is created from an existing class, inheriting all the fields and methods of the parent class.

Question 10. What is the final keyword in Java?

Answer:

The final keyword in Java is used to create constants or to prevent a class, method, or variable from being modified.

Question 11. What is a static method in Java?

Answer:

A static method in Java is a method that belongs to the class and not to any instance of the class.

Question 12. What is a static variable in Java?

Answer:

A static variable in Java is a variable that belongs to the class and not to any instance of the class.

Question 13. What is a package in Java?

Answer:

A package in Java is a mechanism for organizing related classes and interfaces.

Question 14. What is a thread in Java?

Answer:

A thread in Java is a lightweight process that runs concurrently with other threads within a program.

Question 15. What is synchronization in Java?

Answer:

Synchronization in Java is the process of controlling access to shared resources to prevent multiple threads from accessing the same resource simultaneously.

Question 16. What is the difference between ArrayList and LinkedList?

Answer:

An ArrayList is a dynamic array that can resize itself as elements are added or removed. A LinkedList is a linked list that provides constant-time insertions and deletions at any position.

Question 17. What is a HashMap in Java?

Answer:

A HashMap in Java is a data structure that stores key-value pairs in a hash table, allowing fast access to values based on their keys.

Question 18. What is an exception in Java?

Answer:

An exception in Java is an object that represents an error or abnormal condition that occurs during program execution.

Question 19. What is a try-catch block in Java?

Answer:

A try-catch block in Java is used to handle exceptions. Code that might throw an exception is enclosed in a try block, and any exceptions that are thrown are caught and handled in a catch block.

Question 20. What is a finally block in Java?

Answer:

A finally block in Java is a block of code that is always executed, regardless of whether an exception is thrown or not. It is typically used to release resources that were acquired in a try block.

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