Top Java Interview Questions & Answers

1️⃣ What is Java?

Answer:
Java is a high-level, object-oriented, and platform-independent programming language developed by Sun Microsystems (now owned by Oracle).

👉 Java programs can run on any system that has a JVM (Java Virtual Machine).

2️⃣ Why is Java platform independent?

Answer:
Java is platform independent because:

• Java code is compiled into bytecode

• Bytecode runs on JVM

• JVM is available for different operating systems

👉 Write Once, Run Anywhere is the key feature of Java.

3️⃣ What is JVM?

Answer:
JVM (Java Virtual Machine) is responsible for:

• Loading Java bytecode

• Converting bytecode into machine code

• Running Java programs

4️⃣ Difference between JDK, JRE, and JVM

Answer:

5️⃣ What are features of Java?

Answer:

• Platform independent

• Object-oriented

• Secure

• Robust

• Multithreaded

• High performance

6️⃣ What is Object-Oriented Programming (OOP)?

Answer:
OOP is a programming approach based on objects and classes.

Java supports OOP concepts like:

• Encapsulation

• Inheritance

• Polymorphism

• Abstraction

7️⃣ What is a Class?

Answer:
A class is a blueprint used to create objects.
It contains:

• Variables (data)

• Methods (functions)

8️⃣ What is an Object?

Answer:
An object is an instance of a class.
It represents real-world entities and can access class methods and variables.

9️⃣ What is Inheritance?

Answer:
Inheritance allows one class to reuse the properties of another class using the extends keyword.

👉 It helps in code reusability.

🔟 What is Polymorphism?

Answer:
Polymorphism means many forms.
In Java, it allows methods to behave differently based on the object.

Example:

• Method Overloading

• Method Overriding

1️⃣1️⃣ What is Encapsulation?

Answer:
Encapsulation is the process of wrapping data and methods together using classes.

👉 Achieved using private variables and public getters/setters.

1️⃣2️⃣ What is Abstraction?

Answer:
Abstraction hides implementation details and shows only essential features.

👉 Achieved using:

• Abstract classes

• Interfaces

1️⃣3️⃣ What is an Interface?

Answer:
An interface contains only abstract methods (Java 8 onwards allows default methods).

👉 Used to achieve 100% abstraction.

1️⃣4️⃣ What is the difference between == and .equals()?

Answer:

• == compares memory location

• .equals() compares content/value

1️⃣5️⃣ What is a Constructor?

Answer:
A constructor is a special method used to initialize objects.

Rules:

• Same name as class

• No return type