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Class & Object in Java - Java Notes in English Notes

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• Subject Focus: Java Notes in English (BCA / B.Tech Syllabus)

• Core Topic: Class & Object in Java - General Topics

• Overview: Class and Object in Java Class and Object are the foundational pillars of Object-Oriented Programming (OOP). Understanding their relationship is key to...

• Key Concepts: Class और Object in Hindi, Class क्या है, Object क्या है, Class और Object का अंतर, OOP concepts in Hindi, Class और Object का उपयोग, Object Oriented Programming,

Class and Object in Java

Class and Object are the foundational pillars of Object-Oriented Programming (OOP). Understanding their relationship is key to writing Java programs.

Analogy: Blueprint and Houses

Think of a class as an architect's blueprint for a house. The blueprint defines all the properties (e.g., number of rooms, color of walls) and behaviors (e.g., open door, switch on lights) a house can have. The blueprint itself is just a plan; you can't live in it.

An object is an actual house built from that blueprint. It is a real, tangible entity that exists in the world (or in memory). You can build many houses (objects) from the same blueprint (class), and each house will be a unique instance with its own specific properties (e.g., one house is red, another is blue).

1. Class: The Blueprint

A class is a template or user-defined data type.
It defines a set of attributes (fields or variables) and behaviors (methods).
It is a logical entity; it does not occupy memory space until an object is created from it.


// This is the blueprint for a Dog
class Dog {
    // Attributes (state)
    String name;
    String breed;

    // Behavior (methods)
    void bark() {
        System.out.println("Woof!");
    }
    void wagTail() {
        System.out.println(name + " is wagging its tail.");
    }
}

2. Object: The Instance

An object is an instance of a class.
It is a physical entity that has state (values for its attributes) and behavior (defined by its class methods).
When an object is created using the new keyword, memory is allocated for it on the heap.


public class Main {
    public static void main(String[] args) {
        // Create two Dog objects (two houses from the blueprint)
        Dog dog1 = new Dog();
        dog1.name = "Buddy";
        dog1.breed = "Golden Retriever";
        
        Dog dog2 = new Dog();
        dog2.name = "Lucy";
        dog2.breed = "Poodle";

        // Call their methods
        dog1.wagTail(); // Outputs "Buddy is wagging its tail."
        dog2.wagTail(); // Outputs "Lucy is wagging its tail."
    }
}

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Class and Object in Java Class and Object are the foundational pillars of Object-Oriented Programming (OOP).

Understanding Class & Object in Java is fundamental to mastering Java Notes in English. It covers crucial concepts, solved problems, and revision points essential for academic and entrance exam success.

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Class & Object in Java

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Class and Object in Java

Frequently Asked Questions (FAQs)

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