✅ Top Java Interview Questions with Answers: Part-1 ☕

1️⃣ What are the main features of Java?
– Object-Oriented: Everything is an object
– Platform-Independent: Write Once, Run Anywhere (via JVM)
– Simple Secure: Easy syntax + built-in security features
– Multithreaded: Supports concurrent execution
– Robust: Handles errors using exception handling
– High Performance: Through Just-In-Time (JIT) compiler
– Distributed: Can build networked applications using RMI, EJB

2️⃣ Difference between JDK, JRE, and JVM
– JDK (Java Development Kit): Includes tools to develop Java programs (compiler, debugger, etc.)
– JRE (Java Runtime Environment): Runtime for executing Java apps, includes JVM + libraries
– JVM (Java Virtual Machine): Executes Java bytecode; platform-dependent

3️⃣ What is the Java Virtual Machine (JVM)?
JVM is a virtual engine that runs Java bytecode on your machine. It converts .class files to machine code during runtime and handles memory, security, and garbage collection.

4️⃣ Explain the concept of Object-Oriented Programming in Java
Java uses OOP principles:
• Encapsulation: Data hiding using classes
• Inheritance: One class inherits from another
• Polymorphism: One interface, many implementations
• Abstraction: Hiding complexity via abstract classes or interfaces

5️⃣ What is the difference between == and .equals()?
– ==: Compares object references (memory address)
– .equals(): Compares actual content/data of the objects (overridden in String, etc.)

6️⃣ What are access modifiers in Java?
They control visibility of classes, methods, and variables:
• public: Accessible everywhere
• private: Only within the same class
• protected: Within same package + subclasses
• (default): Only within the same package

7️⃣ Difference between abstract class and interface
Abstract Class:
• Can have method bodies
• Can declare constructors
• Supports single inheritance
• Suitable for shared base logic

Interface:
• Only method signatures (till Java 7)
• Cannot have constructors
• Supports multiple interfaces
• Suitable for contract-based design

8️⃣ What is a constructor? Types of constructors?
Constructor is a special method used to initialize objects.
• Default Constructor: No parameters
• Parameterized Constructor: Accepts arguments
It’s called automatically when an object is created.

9️⃣ What is method overloading and overriding?
– Overloading: Same method name, different parameters (within same class)
– Overriding: Redefining superclass method in subclass with same signature

🔟 What is the difference between static and non-static methods?
– Static Method: Belongs to the class, can be called without creating an object
– Non-static Method: Belongs to an instance; requires object creation to access
Static methods can’t directly access instance variables.

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