Java Interview Questions (Fresher)

Top 30+ Java Interview Questions for Freshers with Detailed Answers

Looking for the most asked Java interview questions for freshers? This detailed list covers essential Java concepts and common questions asked in recent coding interviews for entry-level candidates. These Java interview questions for freshers include easy, medium, and advanced questions designed to help you ace your interviews and build strong foundational knowledge in Java programming.

Easy Java Interview Questions for Freshers

1. What is Java? What are the key features of Java?

Java is a high-level, object-oriented, platform-independent programming language. Its key features include portability via the JVM, automatic memory management (garbage collection), strong security, multithreading, and robustness.

2. What do you understand by JVM, JRE, and JDK?

JVM (Java Virtual Machine) runs Java bytecode. JRE (Java Runtime Environment) includes JVM and libraries to run Java programs. JDK (Java Development Kit) contains JRE plus development tools like the compiler.

3. What is the difference between JDK and JRE?

JDK includes tools to develop Java applications (compiler, debugger), whereas JRE only allows you to run Java programs.

4. What are the main data types in Java?

Java has eight primitive data types: byte, short, int, long, float, double, char, and boolean.

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

== compares object references (memory addresses), whereas equals() compares object content for equality.

6. What is a class and object in Java?

A class is a blueprint for objects defining properties and behaviors. An object is an instance of a class.

7. What is inheritance?

Inheritance allows a class (subclass) to acquire properties and methods from another class (superclass), promoting code reuse.

8. What are constructors in Java?

Constructors are special methods used to initialize new objects. They have the same name as the class and no return type.

9. What is the difference between method overloading and method overriding?

Overloading is defining multiple methods with the same name but different parameters in the same class. Overriding is redefining a superclass method in a subclass.

10. What are access modifiers in Java?

Access modifiers control visibility: public, private, protected, and default (package-private).

11. What is the use of the ‘final’ keyword?

‘final’ restricts modification. It can make variables constants, prevent method overriding, or inheritance of classes.

12. What is an interface in Java?

An interface defines abstract methods that classes can implement. It provides multiple inheritance in Java.

Medium Java Interview Questions for Freshers

13. What is the difference between Abstract Class and Interface?

Abstract classes can have implemented methods and state, interfaces can only declare methods (until Java 8). Classes can implement multiple interfaces but inherit only one class.

14. What is the purpose of the ‘static’ keyword?

‘static’ makes variables or methods belong to the class rather than any instance.

15. Explain Java Exception Handling.

Java handles exceptions using try-catch blocks, allowing the program to continue execution by catching and handling errors.

16. What is the difference between Checked and Unchecked Exceptions?

Checked exceptions are checked at compile-time (e.g., IOException), unchecked exceptions occur at runtime (e.g., NullPointerException).

17. What is multithreading in Java?

Multithreading allows concurrent execution of two or more threads to maximize CPU usage.

18. What are the main benefits of multithreading?

Improved performance and resource utilization, better program structure, and responsiveness.

19. What is the difference between ‘wait()’ and ‘sleep()’ methods?

‘wait()’ releases the object lock and waits to be notified. ‘sleep()’ pauses thread without releasing locks.

20. What are collections in Java?

Collections framework provides data structures like List, Set, Map to store and manipulate groups of objects.

21. What is the difference between ArrayList and LinkedList?

ArrayList uses a dynamic array internally, fast random access; LinkedList uses a doubly-linked list, faster insertions/deletions.

22. What is a Java Stream?

Streams represent sequences of elements supporting aggregate operations like filter, map, and reduce for functional-style processing.

23. How does Garbage Collection work in Java?

Java automatically frees memory used by objects no longer referenced by the program using garbage collection algorithms.

Advanced Questions for Freshers

24. What is the Java Memory Model?

It defines how Java manages memory, including heap, stack, method area, and how threads interact with memory.

25. Explain the difference between HashMap and Hashtable.

HashMap is unsynchronized and allows null keys/values; Hashtable is synchronized and does not allow null keys or values.

26. What are Java Annotations?

Annotations provide metadata for code, used for documentation, compile-time checks, or runtime processing.

27. What is the difference between StringBuilder and StringBuffer?

Both are used to create mutable strings, but StringBuffer is synchronized (thread-safe) and StringBuilder is faster but not thread-safe.

28. What is the purpose of the ‘transient’ keyword?

‘transient’ marks variables to be skipped during serialization.

29. What is serialization in Java?

Serialization is the process of converting an object into a byte stream to save or transmit it.

30. What are Functional Interfaces?

Interfaces with a single abstract method, used in lambda expressions and method references.

31. What is the difference between final, finally, and finalize?

final is a keyword to restrict modification, finally is a block executed after try/catch, and finalize() is a method called by GC before object destruction.

32. How do you handle synchronization in Java?

Using the synchronized keyword to control access to critical sections or objects to prevent thread interference.

These Java interview questions for freshers provide a strong foundation and help you prepare thoroughly for entry-level Java interviews.