Core Java Interview Questions (Basic Level)
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.
