What is Inheritance in Java?

Inheritance is one of the core concepts of Object-Oriented Programming (OOP) in Java. It allows a class (child or subclass) to inherit properties and behaviors (fields and methods) from another class (parent or superclass).

Syntax:

class Parent {
    // fields and methods
}

class Child extends Parent {
    // additional fields and methods
}

• extends: keyword used to inherit a class

Why Use Inheritance?

• Code Reusability – Write once, reuse in multiple places
• Organized Code – Common logic in base class, specific logic in child class
• Polymorphism Support – One interface, multiple behaviors

Types of Inheritance in Java:

1. Single Inheritance
2. Multilevel Inheritance
3. Hierarchical Inheritance
4. (Java does not support multiple inheritance with classes directly but supports it through interfaces)

Example 1: Single Inheritance

// Parent class
class Animal {
    void eat() {
        System.out.println("This animal eats food.");
    }
}

// Child class
class Dog extends Animal {
    void bark() {
        System.out.println("Dog barks.");
    }
}

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

Output:

This animal eats food.
Dog barks.

Example 2: Multilevel Inheritance

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

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

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

public class Main {
    public static void main(String[] args) {
        Puppy p = new Puppy();
        p.eat();
        p.bark();
        p.weep();
    }
}

Output:

Eating...
Barking...
Weeping...

Example 3: Hierarchical Inheritance

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

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

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

public class Main {
    public static void main(String[] args) {
        Cat c = new Cat();
        Dog d = new Dog();
        c.sound();
        c.meow();
        d.sound();
        d.bark();
    }
}

Output:

Animal makes sound
Cat meows
Animal makes sound
Dog barks

Important Keyword: super

The super keyword is used to:

• Refer to the parent class constructor
• Access parent class methods or fields

Example:

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

class Dog extends Animal {
    void sound() {
        super.sound();  // calls parent method
        System.out.println("Dog barks");
    }
}

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

Output:

Animal sound
Dog barks

Java Doesn’t Support Multiple Inheritance (with classes)

// This will cause an error in Java
class A { }
class B { }
class C extends A, B { } // Not allowed

👉 Use interfaces instead for multiple inheritance.

Summary Table: