Top 20 Java Interview Questions You Need to Know
- Sreenivas Mathala
- Dec 31, 2024
- 3 min read
Updated: Jan 12
Java Interview Questions and Answers
1. What is Java?
Answer: Java is a high-level, object-oriented programming language designed to be platform-independent through the use of the Java Virtual Machine (JVM). Its key features include portability, security, and robustness.
2. Explain the Key Features of Java
Answer:
Platform Independence: Write once, run anywhere (WORA).
Object-Oriented: Supports encapsulation, inheritance, and polymorphism.
Automatic Memory Management: Uses garbage collection.
Multithreading: Supports concurrent execution of two or more threads.
3. What are JDK, JRE, and JVM?
Answer:
JDK (Java Development Kit): A software development kit for developing Java applications.
JRE (Java Runtime Environment): Provides libraries and components to run Java applications.
JVM (Java Virtual Machine): An engine that executes Java bytecode.
4. What is a Class in Java?
Answer: A class is a blueprint for creating objects. It encapsulates data for the object and methods to manipulate that data.
5. Explain the “Main” Method in Java
Answer: The main method is the entry point of any Java application. It must be declared as public static void main(String[] args).
6. What are Constructors in Java?
Answer: Constructors are special methods used to initialize objects. They have the same name as the class and do not have a return type.
7. What is Inheritance in Java?
Answer: Inheritance allows one class to inherit fields and methods from another class, promoting code reusability.
8. What are Access Modifiers in Java?
Answer:
Public: Accessible from any other class.
Private: Accessible only within its own class.
Protected: Accessible within its own package and by subclasses.
9. Difference Between “==” and “.equals()” in Java?
Answer: == checks for reference equality (whether both references point to the same object), while .equals() checks for value equality (whether two objects are logically equivalent).
10. Explain Method Overloading in Java
Answer: Method overloading allows multiple methods with the same name but different parameters (type or number) within the same class.
11. What is the “this” Keyword in Java?
Answer: The this keyword refers to the current instance of a class, used to avoid ambiguity between instance variables and parameters.
12. What is a Static Method in Java?
Answer: A static method belongs to the class rather than any instance of the class and can be called without creating an object of the class.
13. What is an Abstract Class in Java?
Answer: An abstract class cannot be instantiated and may contain abstract methods (without implementation) that must be implemented by subclasses.
14. Discuss the Significance of the “final” Keyword in Java
Answer:
When applied to a variable, it makes it constant.
When applied to a method, it prevents overriding.
When applied to a class, it prevents inheritance.
15. What is an Interface in Java?
Answer: An interface defines a contract that classes can implement. It can contain abstract methods and constants but cannot contain method implementations until Java 8 introduced default methods.
16. What are Collections in Java?
Answer: Collections are frameworks that provide an architecture to store and manipulate groups of objects efficiently, including lists, sets, and maps.
17. Explain Exception Handling in Java
Answer: Exception handling is a mechanism to handle runtime errors using try, catch, finally, and throw keywords to maintain normal application flow.
18. What is Multithreading in Java?
Answer: Multithreading allows concurrent execution of two or more threads within a program, improving performance by utilizing CPU resources effectively.
19. How do you create a Thread in Java?
Answer: You can create a thread by extending the Thread class or implementing the Runnable interface.
class MyThread extends Thread {
public void run() {
System.out.println("Thread running");
}
}20. What is Garbage Collection in Java?
Answer: Garbage collection is an automatic memory management process that identifies and discards objects that are no longer needed by a program, freeing up memory space.
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