Core Java Interview Questions

1. What is Java?

Java is a high-level, object-oriented, platform-independent programming language developed by Sun

Microsystems.

2. What are the features of Java?

 Object-Oriented

 Platform Independent (via JVM)

 Secure and Robust

 Multithreaded

 Architecture Neutral

 High Performance (via JIT compiler)

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

 JDK: Java Development Kit – tools to develop and compile Java code.

 JRE: Java Runtime Environment – environment to run Java applications.

 JVM: Java Virtual Machine – executes bytecode on different machines.

4. What are data types in Java?

 Primitive: int, byte, short, long, float, double, char, boolean

 Non-Primitive: Arrays, Classes, Interfaces, Strings

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

 == compares object references.

 .equals() compares actual values of objects.

6. What is a constructor in Java?

A constructor is a special method used to initialize objects. It has the same name as the class and no

return type.

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

 Overloading: Same method name, different parameters (within same class).

 Overriding: Same method name and parameters (in child class).

8. What are access modifiers in Java?

 public: Accessible from everywhere.

 private: Accessible only within the class.

 protected: Accessible within package and subclasses.

 default (no modifier): Accessible within package only.

9. What is the difference between ArrayList and LinkedList?

 ArrayList: Faster for read operations, uses index.

 LinkedList: Faster for insert/delete operations.

10. What is an interface in Java?

An interface is a reference type that contains only abstract methods (before Java 8). Used for

abstraction and multiple inheritance.

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