Top 10 Java Interview Questions and Answers

1.  What is the difference between == and .equals() in Java?

  • == is used to compare reference equality, i.e., whether two objects refer to the same memory location.
  • .equals() is a method used to compare content equality, i.e., whether two objects have the same content.

2. What is the difference between ArrayList and LinkedList in Java?

  • ArrayList internally uses a dynamic array to store elements, allowing fast random access but slower insertion and deletion.
  • LinkedList internally uses a doubly linked list, providing fast insertion and deletion but slower random access.

3. Explain the concept of inheritance in Java.

  • Inheritance allows a class (subclass) to inherit properties and behaviors from another class (superclass).
  • Subclasses can extend the functionality of the superclass by adding new methods or overriding existing ones.

4. What is the difference between interface and abstract class in Java?

  • An interface only contains abstract methods and constants, whereas an abstract class can have both abstract and concrete methods.
  • A class can implement multiple interfaces but can only extend one abstract class.

5. What is a constructor in Java?

  • A constructor is a special method used to initialize objects of a class.
  • It has the same name as the class and does not have a return type.
  • Constructors can be parameterized or default (no-argument).

6. Explain the static keyword in Java.

  • static is a keyword used to declare members (variables and methods) that belong to the class rather than instances of the class.
  • Static members are shared among all instances of the class and can be accessed using the class name.

7. What is method overloading and method overriding in Java?

  • Method overloading is the process of defining multiple methods in a class with the same name but different parameters.
  • Method overriding occurs when a subclass provides a specific implementation for a method that is already defined in its superclass.

8. What is the difference between final, finally, and finalize in Java?

  • final is a keyword used to declare constants, prevent method overriding, or make a class immutable.
  • finally is a block used to execute code after a try-catch block, ensuring that cleanup code is always executed, regardless of whether an exception occurs.
  • finalize is a method called by the garbage collector before reclaiming an object’s memory; however, it’s generally not recommended to rely on it for resource cleanup.

9. Explain the concept of multithreading in Java.

  • Multithreading allows concurrent execution of multiple threads within a single process.
  • Java provides built-in support for multithreading through the Thread class or by implementing the Runnable interface.

10. What is the try-with-resources statement in Java?

  • The try-with-resources statement is used to automatically close resources (such as streams, readers, or connections) that are opened within its block.
  • It ensures that resources are closed properly, even if an exception occurs, by automatically invoking the close() method of each resource.

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