Java/Inheritance and Polymorphism

One of the most effective concepts of OOPs is because it provides the hierarichical classifications and we can create a general class and can be inherited by other classes.

The class which is inherited as defined as “ Super Class” and other classes which inherit the super class is called “Sub class”. A subclass is a specialized version of a Superclass which inherits all of the instance variables and methods defined by the superclass and adds its own, unique elements.

Java provides us a keyword “Extends” which helps the super class to be inherited by the other sub class.

The following program creates a superclass called A and a subclass called B. Notice how the keyword extends is used to create a subclass of A.

public class InheritanceExample {
 
	public static void main(String[] args) {
 
		B b = new B();
 
		// showij is not defined in class B
		// but in class A and still class B
		// is able to call it. This is 
		// called inheritence.
		b.showij();
		b.showk();
		b.sum();
	}
}
 
class A {
	int i = 3;
	int j = 5;
 
	void showij() {
		System.out.println("i and j: " + i + " " + j);
	}
}
 
// Class B is a subclass of Class A.
class B extends A {
	int k = 10;
 
	void showk() {
		System.out.println("k: " + k);
	}
 
	void sum() {
		System.out.println("i+j+k: " + (i + j + k));
	}
}

public class PolymorphismExample {
 
	public static void main(String[] args) {
		Mammal mammal = new Dog();
		mammal.sound();
 
		mammal = new Cat();
		mammal.sound();
	}
}
 
interface Mammal {
 
	public void sound();
}
 
class Dog implements Mammal {
 
	public void sound() {
 
		System.out.println("Dog Barks.");
	}
 
 
}
 
class Cat implements Mammal {
 
	public void sound() {
 
		System.out.println("Cat Mews.");
	}
 
}