Top 25 Java Interview Questions and Answers for Freshers

Preparing for a Java interview? Here are the most frequently asked Java interview questions tailored for beginners and freshers. These questions cover core concepts like OOPs, data types, collections, exception handling, and more.

1️⃣ What is Java?

Java is a high-level, object-oriented programming language developed by Sun Microsystems. It is platform-independent due to the Java Virtual Machine (JVM).

2️⃣ What are the features of Java?

Object-Oriented
Platform Independent
Simple and Secure
Multithreaded
Robust and Portable

3️⃣ What is the difference between JDK, JRE, and JVM?

JDK: Java Development Kit – full suite for development.
JRE: Java Runtime Environment – to run Java programs.
JVM: Java Virtual Machine – engine that runs the code.

4️⃣ What is a Class and an Object?

Class is a blueprint; Object is an instance of the class.

5️⃣ What is Inheritance in Java?

Inheritance allows one class to acquire properties and methods of another. Java supports single inheritance using the extends keyword.

6️⃣ What is Polymorphism?

It allows objects to take many forms — method overloading and overriding are examples.

7️⃣ Difference between Method Overloading and Overriding?

Overloading: Same method name, different parameters (within the same class).
Overriding: Subclass redefines a parent class method.

8️⃣ What is Encapsulation?

Wrapping data and methods together using private variables and public getters/setters.

9️⃣ What is Abstraction?

Hiding internal details and showing only essential information using abstract classes or interfaces.

🔟 What are Constructors?

Special methods that initialize objects. They have the same name as the class and no return type.

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

== compares reference; equals() compares values.

1️⃣2️⃣ What is the use of ‘final’ keyword?

It can be used with variables (constants), methods (cannot override), and classes (cannot inherit).

1️⃣3️⃣ What is an Array in Java?

A container object that holds a fixed number of elements of a single type.

1️⃣4️⃣ What is a String in Java?

Strings are objects representing sequences of characters. They are immutable.

1️⃣5️⃣ Difference between String, StringBuilder, and StringBuffer?

String: Immutable
StringBuilder: Mutable, not thread-safe
StringBuffer: Mutable, thread-safe

1️⃣6️⃣ What is Exception Handling?

Mechanism to handle runtime errors using try-catch-finally blocks.

1️⃣7️⃣ Checked vs Unchecked Exceptions?

Checked: Caught at compile time (e.g., IOException)
Unchecked: Occur at runtime (e.g., NullPointerException)

1️⃣8️⃣ What are Java Collections?

A framework to store and manipulate groups of objects like List, Set, Map, etc.

1️⃣9️⃣ What is the difference between ArrayList and LinkedList?

ArrayList: Fast for access, slow for insert/delete.
LinkedList: Fast for insert/delete, slow for access.

2️⃣0️⃣ What is a HashMap?

Stores data in key-value pairs. Keys are unique, values can be duplicated.

2️⃣1️⃣ What is Multithreading?

Executing multiple threads simultaneously to achieve parallelism.

2️⃣2️⃣ What is the difference between process and thread?

Process is an independent program; thread is a lightweight subprocess.

2️⃣3️⃣ What is a Wrapper Class?

Wrapper classes convert primitives into objects (e.g., int → Integer).

2️⃣4️⃣ What is Autoboxing and Unboxing?

Automatic conversion between primitive types and wrapper classes.

2️⃣5️⃣ What is the default value of local variables?

Local variables must be initialized before use. No default value is assigned.

🧠 Pro Tip

Focus on concepts, write simple code snippets, and practice pattern/array/string problems regularly.

📌 Conclusion

These Java interview questions will help freshers prepare confidently. Keep practicing and dive deeper into real-world Java problems!

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