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☕ Java Lesson – Inheritance

Is lesson me hum seekhenge:

  • Inheritance kya hai
  • Types of inheritance
  • Syntax aur keywords
  • Superclass aur Subclass
  • Method overriding
  • Example programs

📌 Inheritance Kya Hai?

  • Inheritance = ek class ka dusre class se properties aur methods inherit karna
  • Reusability aur maintainability improve hoti hai
  • Parent class = Superclass, Child class = Subclass

Syntax

class SuperClass {
    // members
}

class SubClass extends SuperClass {
    // members of SubClass + inherited members
}

📌 Types of Inheritance in Java

  1. Single Inheritance – Ek parent aur ek child class
  2. Multilevel Inheritance – Chain of classes
  3. Hierarchical Inheritance – Ek parent multiple child classes
  4. Multiple Inheritance – Java me class ke liye direct multiple inheritance nahi hota, interface se possible

1️⃣ Example – Single Inheritance

class Animal {
    void eat(){
        System.out.println("Animal is eating");
    }
}

class Dog extends Animal {
    void bark(){
        System.out.println("Dog is barking");
    }
}

public class SingleInheritanceExample {
    public static void main(String[] args){
        Dog d = new Dog();
        d.eat();  // inherited method
        d.bark(); // own method
    }
}

Output:

Animal is eating
Dog is barking

2️⃣ Example – Multilevel Inheritance

class Animal {
    void eat(){
        System.out.println("Animal is eating");
    }
}

class Dog extends Animal {
    void bark(){
        System.out.println("Dog is barking");
    }
}

class Puppy extends Dog {
    void weep(){
        System.out.println("Puppy is weeping");
    }
}

public class MultilevelInheritance {
    public static void main(String[] args){
        Puppy p = new Puppy();
        p.eat();  // inherited from Animal
        p.bark(); // inherited from Dog
        p.weep(); // own method
    }
}

Output:

Animal is eating
Dog is barking
Puppy is weeping

3️⃣ Example – Hierarchical Inheritance

class Animal {
    void eat(){
        System.out.println("Animal is eating");
    }
}

class Dog extends Animal {
    void bark(){
        System.out.println("Dog is barking");
    }
}

class Cat extends Animal {
    void meow(){
        System.out.println("Cat is meowing");
    }
}

public class HierarchicalInheritance {
    public static void main(String[] args){
        Dog d = new Dog();
        Cat c = new Cat();

        d.eat();
        d.bark();

        c.eat();
        c.meow();
    }
}

Output:

Animal is eating
Dog is barking
Animal is eating
Cat is meowing

4️⃣ Super Keyword

  • super → parent class ka reference
  • Use: access parent class members/methods/constructor

Example – Super Keyword

class Animal {
    void eat(){
        System.out.println("Animal is eating");
    }
}

class Dog extends Animal {
    void eat(){
        System.out.println("Dog is eating");
    }

    void show(){
        eat();       // Dog's eat()
        super.eat(); // Animal's eat()
    }
}

public class SuperExample {
    public static void main(String[] args){
        Dog d = new Dog();
        d.show();
    }
}

Output:

Dog is eating
Animal is eating

5️⃣ Method Overriding

  • Subclass me parent class method ko redefine karna
  • Same method name, same parameters

Example – Method Overriding

class Animal {
    void sound(){
        System.out.println("Animal makes sound");
    }
}

class Dog extends Animal {
    @Override
    void sound(){
        System.out.println("Dog barks");
    }
}

public class MethodOverridingExample {
    public static void main(String[] args){
        Animal a = new Animal();
        a.sound();

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

Output:

Animal makes sound
Dog barks

⚡ Important Points

  • Inheritance = code reuse aur hierarchical relationship
  • extends keyword = class inheritance
  • super keyword = parent class reference
  • Method overriding = runtime polymorphism
  • Multiple inheritance with classes nahi, interfaces ke saath possible

🎯 Interview Questions

1️⃣ Inheritance kya hai aur use kyun karte hain?
2️⃣ Java me multiple inheritance kaise possible hai?
3️⃣ super keyword ka use kya hai?
4️⃣ Method overriding aur overloading me difference kya hai?
5️⃣ Single, Multilevel, Hierarchical inheritance ka example de sakte hain?

🧾 Lesson Summary

Is lesson me humne seekha:

✔ Inheritance ka concept aur importance
✔ Single, Multilevel, Hierarchical inheritance
✔ super keyword ka use
✔ Method overriding ka example
✔ OOP me code reusability aur hierarchy

Inheritance Java me OOP ka fundamental pillar hai aur large programs me structure aur maintainability improve karta hai.

🚀 Next Lesson

Next lesson me hum seekhenge:

  • Polymorphism
  • Compile-time & Runtime Polymorphism
  • Method Overloading
  • Method Overriding detailed
  • Constructor Overloading