Top 20 Java Interview Questions and Answers for Experienced Developers


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


  • An abstract class can have both abstract and concrete methods, whereas an interface can only have abstract methods.
  • A class can extend only one abstract class but implement multiple interfaces.
  • Abstract classes can have constructors, while interfaces cannot.

2. Explain the concept of multithreading in Java.

Multithreading in Java allows multiple threads to execute concurrently. It helps in achieving better performance and responsiveness. Java provides built-in support for multithreading using the Thread class or the Runnable interface.

3. What is the purpose of the volatile keyword in Java?

The volatile keyword is used to declare a variable as volatile, ensuring that reads and writes to the variable are directly performed on the main memory. It prevents thread-specific caching of the variable’s value and is often used for variables accessed by multiple threads.

4. How does Java handle memory management, and what is the role of the JVM’s garbage collector?

Java uses automatic memory management. The JVM’s garbage collector identifies and reclaims memory that is no longer in use, preventing memory leaks. It tracks object references, reclaiming memory when objects are no longer reachable.

5. Explain the differences between equals() and == in Java.


  • equals(): This method is used to compare the content (values) of objects. It’s typically overridden in classes to provide custom comparison logic.
  • ==: This operator is used to compare object references. It checks whether two references point to the same memory location.

6. What is the difference between throw and throws in Java?


  • throw: It is used to throw an exception explicitly in a method.
  • throws: It is used in method signatures to declare exceptions that may be thrown by the method but are not caught inside the method. The caller of the method is responsible for handling these exceptions.

7. How does Java support multiple inheritance, and what is the interface used for?

Java supports multiple inheritance through interfaces. An interface is a contract that defines a set of abstract methods. A class can implement multiple interfaces, allowing it to inherit the method signatures from those interfaces.

8. What is the purpose of the transient keyword in Java?

The transient keyword is used to indicate that a variable should not be serialized when an object is converted to a byte stream (for example, during object serialization). It’s often used for variables that don’t need to be persisted.

9. Explain the try-catch-finally block in exception handling.

The try block is used to enclose code that may throw exceptions. If an exception occurs, the control is transferred to the catch block that matches the exception type. The finally block is used for code that needs to be executed regardless of whether an exception was thrown or not.

10. What is the purpose of the static keyword in Java?

The static keyword is used to create class-level variables and methods, which can be accessed without creating an instance of the class. It is often used for constants, utility methods, and shared resources.

11. Explain the concept of the toString() method in Java.

The toString() method is used to return a string representation of an object. It is often overridden in classes to provide a meaningful string representation of an object.

12. What is the super keyword in Java, and how is it used?

The super keyword is used to refer to the superclass (parent class) of a subclass. It can be used to call the superclass’s constructor, methods, or access its members in the context of the subclass.

13. What are lambda expressions, and how are they used in Java?

Lambda expressions are a feature introduced in Java 8 to enable the concise representation of anonymous functions. They are used to implement functional interfaces (interfaces with a single abstract method) and simplify the use of functional programming constructs in Java.

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


  • ArrayList: It is implemented as a dynamic array and provides fast random access to elements.
  • LinkedList: It is implemented as a doubly-linked list and is efficient for insertions and deletions, especially when elements are frequently added or removed from the middle of the list.

15. Explain the concept of Java generics and how they are used.

Generics in Java allow you to create classes, interfaces, and methods that operate on specified data types without the need for casting. They provide type safety and help in writing reusable and flexible code.

16. What is method overloading in Java?

Method overloading is the ability to define multiple methods with the same name in the same class but with different parameter lists. The compiler determines which method to call based on the number and types of arguments passed.

17. What is the this keyword in Java, and how is it used?

The this keyword refers to the current instance of the class. It is used to access instance variables and methods within the class. It is often used to disambiguate between instance variables and method parameters with the same names.

18. How does exception chaining work in Java, and what is the getCause() method used for?

Exception chaining allows one exception to be wrapped inside another. The getCause() method is used to retrieve the underlying exception that caused the current exception. This feature is useful for preserving the original context of an exception.

19. What is the purpose of the finalize() method in Java?

The finalize() method is called by the garbage collector before an object is reclaimed. It can be overridden in a class to perform cleanup operations, but it is not recommended to rely on it for resource management.

20. Explain the concept of method references in Java 8 and how they simplify code.

Method references are a shorthand notation for lambda expressions that reference methods by name. They simplify code by reducing the verbosity of lambda expressions and making the code more readable. Method references can be categorized into four types: static, instance, constructor, and arbitrary object method references.

These questions and answers should help you prepare for your Java interview as an experienced developer. Be sure to delve deeper into each topic and practice coding examples to solidify your understanding. Good luck with your interview!

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I, Manohar am the founder and chief editor of I am working in an IT professional.

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