Classes and Objects in Java

Class aur Object Kya Hote Hain?

Class – Design/Blueprint

Class ek blueprint hota hai. Jaise architect ke paas ek ghar banane ka design hota hai, waise hi class ek template hai jisse object bante hain.

class Car {
    // Properties
    String color;
    String model;

    // Behavior (Method)
    void drive() {
        System.out.println("Car is moving...");
    }
}

Object – Real Entity

Object class ka real-world version hota hai. Class ek idea hai, aur object us idea ka implementation.

Car myCar = new Car(); // myCar is an object of class Car

Real-Life Example

Class: Ghar ka naksha (blueprint)

Object: Real ghar jo ban gaya hai

Note: Ek class se hum multiple objects bana sakte hain – jaise ek design se 100 ghar ban sakte hain.

Class Declaration – Syntax:

class ClassName {
  // variables (attributes)
  // methods (functions)
}

Example:

class Student {
    String name;
    int age;

    void study() {
        System.out.println(name + " is studying");
    }
}

Object Creation – Syntax

ClassName objectName = new ClassName();

Object Example:

Student s1 = new Student(); // s1 is object of Student
s1.name = "Arun";
s1.age = 21;
s1.study();  // Output: Shakib is studying

Multiple Objects from One Class

Student s2 = new Student();
s2.name = "Ravi";
s2.age = 22;
s2.study(); // Output: Ravi is studying

Output:

Shakib is studying  
Arun is studying

Memory Concept (How JVM handles it)

• Class ka code memory mein ek baar load hota hai.
• Har object ke liye alag memory allocate hoti hai.
• Methods shared hote hain, but variables object-specific hote hain.

Practice Task (Try This)

java
CopyEdit
class Book {
    String title;
    String author;

    void showDetails() {
        System.out.println("Book: " + title + ", Author: " + author);
    }

    public static void main(String[] args) {
        Book b1 = new Book();
        b1.title = "Atomic Habits";
        b1.author = "James Clear";
        b1.showDetails();
    }
}

Points to Remember

1. Class: Blueprint ya template
2. Object: Class ka real-world instance
3. Method: Object ka behavior define karta hai
4. Variable: Object ki property ya data hoti hai

Conclusion

Java mein Class aur Object ka concept OOP ki foundation hai. Har Java program directly ya indirectly class aur object se hi bana hota hai.