Is lesson me hum seekhenge:

• Interface kya hota hai
• Interface me method declaration
• Subclass me method body implement karna
• implements keyword
• extends keyword
• Interface aur Abstract Class ka relation
• Interface + Abstract Class example

Interface ek fully abstract blueprint hota hai.

Iska use hota hai:

100% abstraction achieve karne ke liye

Interface me normally hota hai:

method declaration
constants

Interface me methods by default:

public abstract

interface Animal {

    void sound();

}

Ye actually internally hota hai:

interface Animal {

    public abstract void sound();

}

Interface me method sirf declare hota hai, body nahi hoti.

Example

interface Vehicle {

    void start();

    void stop();

}

Yahan:

start()
stop()

sirf declare hue hain.

Interface ko implement karne wali class me methods ki body likhni padti hai.

Example

interface Animal {

    void sound();
}

class Dog implements Animal {

    public void sound(){
        System.out.println("Dog barks");
    }

}

public class Test {

    public static void main(String[] args){

        Dog d = new Dog();
        d.sound();

    }
}

Output

Dog barks

implements keyword use hota hai:

interface ko implement karne ke liye

Example

class Dog implements Animal

Matlab:

Dog class Animal interface ke methods implement karegi

Interface bhi dusre interface ko extend kar sakta hai.

Example

interface Animal {

    void eat();

}

interface Dog extends Animal {

    void bark();

}

Ab Dog interface me:

eat()
bark()

dono methods honge.

Abstract class aur interface saath me use ho sakte hain.

Example

Interface → method rules define karta hai
Abstract class → partial implementation deta hai
Subclass → final implementation deta hai

Example

interface Vehicle {

    void start();

}

abstract class Car implements Vehicle {

    void fuelType(){
        System.out.println("Petrol Car");
    }
}

class BMW extends Car {

    public void start(){
        System.out.println("BMW Starting");
    }

}

public class Test {

    public static void main(String[] args){

        BMW car = new BMW();

        car.start();
        car.fuelType();

    }
}

Output

BMW Starting
Petrol Car

Explanation:

Interface → start() declare
Abstract Class → fuelType() implement
Subclass → start() implement

✔ Interface ka object directly nahi bana sakte

❌

Vehicle v = new Vehicle(); // error

✔ Interface methods by default:

public abstract

✔ Interface variables by default:

public static final

Example

interface Test {

    int number = 10;

}

General structure:

interface InterfaceName {

    method declaration

}

abstract class Parent implements InterfaceName {

}

class Child extends Parent {

    method implementation

}

1️⃣ Interface kya hota hai?
2️⃣ Interface aur abstract class me difference kya hai?
3️⃣ implements keyword ka use kya hai?
4️⃣ Interface method body kaha likhte hain?
5️⃣ Interface interface ko kaise extend karta hai?

Is lesson me humne seekha:

✔ Interface concept
✔ Interface method declaration
✔ Subclass me method implementation
✔ implements keyword
✔ extends keyword
✔ Interface + Abstract class relation

Interface Java me loose coupling aur abstraction achieve karne ke liye bahut important concept hai.