Java Inheritance

Inheritance is the process when a class inherits properties and behavior from another class.

Key Components of inheritances are:

1. Super class: The super-class whose properties and methods are inherited by another class. It also called parent class or base class.

2. Sub class: The sub-class inherits properties and methods from another class. It also called child class or derived class.

3. extends keyword: it is a keyword used for inheritance.

Syntax:

class SubClass extends SuperClass
{
    // class body
}

Example:

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

// Dog is the sub class and Animal is the super class
class Dog extends Animal {
    void bark() {
        System.out.println("The dog barks.");
    }
}

class Main {
    public static void main(String[] args) {
        Dog dog = new Dog();
        dog.eat();  // Inherited method eat from Animal class
    }
}

Types of inheritance in Java:

1. Single inheritance : Above example is single inheritance. In single inheritance the sub class inherits a super class only.

2. Multilevel inheritance.

3. Hierarchical inheritance.

2. Multilevel inheritance:  When a subclass inherits from another subclass called multilevel inheritance.

class ClassA
{
    // class body
}

class ClassB extends ClassA
{
    // class body
}


class ClassC extends ClassB
{
    // class body
}

Example:

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

// Dog Sub Class and Animal Super Class
class Dog extends Animal {
    void bark() {
        System.out.println("The dog barks.");
    }
}

// Puppy Sub Class and Dog Super Class ( which is a sub class of Animal)
class Puppy extends Dog {
    void weep() {
        System.out.println("The puppy weeps.");
    }
}

public class Main {
    public static void main(String[] args) {
        Puppy puppy = new Puppy();
        puppy.eat();  // Inherited method eat from Animal class
        puppy.bark(); // Inherited method bark from Dog class
    }
}

3. Hierarchical inheritance: When multiple subclass inherits from one superclass

class SuperClass
{
    // class body
}

class SubClass1 extends SuperClass
{
    // class body
}


class SubClass2 extends SuperClass
{
    // class body
}

Example:

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

// Dog Sub Class and Animal Super Class
class Dog extends Animal {
    void bark() {
        System.out.println("The dog barks.");
    }
}

// Cat Sub Class and Animal Super Class
class Cat extends Animal {
    void meow() {
        System.out.println("The cat meows.");
    }
}

public class Main {
    public static void main(String[] args) {
        Dog dog = new Dog();
        Cat cat = new Cat();

        dog.eat();  // Inherited method eat from Animal

        cat.eat();  // Inherited method eat from Animal
    }
}