Derived from two Greek words ‘poly’ and ‘morphs ’, the word polymorphism refers to many forms. It is one of the most important concepts in Object-Oriented programming.

There are two forms of Polymorphism in java. These include:

• Runtime polymorphism

• Compile-time polymorphism

Polymorphism allows us to use the same entity i.e a method to perform different actions in different situations. In the example below we are using the same method to perform different actions under the same name.

class AnimalsEat {
    public void eat() {
        System.out.println("All animals eat !");
    }
}
class Cows extends AnimalsEat {
    public void eat() {
        System.out.println("Cows eat grass !");
    }
}
class Dogs extends AnimalsEat {
    public void eat() {
        System.out.println("Dogs eat dog food !");
    }

}

class Main {
    public static void main(String[] args) {
        Cows obj1 = new Cows();
        obj1.eat();

        Dogs obj2 = new Dogs();
        obj2.eat();
    }
}

Output

Cows eat grass !
Dogs eat dog food !

In the code above we have created a superclass named AnimalsEat with the method,eat() from which two subclasses namely: the Dogs class and the Cows class have inherited from.
The method eat() has been used in these two classes to render different messages, this method, therefore, has different forms in these two subclasses.

Now polymorphism can be achieved in three major ways in Java and these include through:

• Method Overloading

• Operator Overloading

• Method Overriding

Method Overloading.

Method overloading is a scenario in Java where a class is allowed to have several methods with the same name provided that these methods have different parameters. Now parameters in these methods can be different in the sense that: the methods have an unequal number of parameters, parameters are of different data types, or the sequence of these parameters varies.

Here is an example:

class AddNumbers {
    public int sum(int a, int b) {
        int result = a + b;
        return result;


    }

    public double sum(double c, double d) {
        double result2 = c + d;
        return result2;

    }


}
class Main {
    public static void main(String[] args) {
        AddNumbers obj = new AddNumbers();
        int result = obj.sum(3, 4);
        System.out.println(result);

        double result2 = obj.sum(34.5, 34.2);
        System.out.println(result2);
    }

}

Output

7
68.7

In the code above we have created a class named AddNumbers, I agree it is not a great choice when it comes to naming a class. However, as you can see we have overloaded the method sum(), by having parameters of different data types. The compiler in this case is responsible for distinguishing the method, and therefore this is known as compile-time polymorphism.

Method Overriding.

Method overriding can be achieved through inheritance in java. Inheritance allows us to derive a new class from a preexisting class. Inheritance also promotes code reusability by allowing one class known as the subclass or child class to inherit methods and fields from another class known as the superclass or the parent class.
Now method overriding occurs when a method is defined with the same name both in the subclass and the superclass. Here is an example of method overriding in java.

class Fruits {
    public void display() {
        System.out.println("Most fruits turn yellow when ripe !");
    }
}
class Oranges extends Fruits {
    @Override
    public void display() {
        System.out.println("Oranges turn yellow when ripe !");
    }
}
class Main {
    public static void main(String[] args) {
        //object for Fruit class
        Fruits obj = new Fruits();
        obj.display();
        //object for Oranges class
        Oranges obj1 =  new Oranges();
        obj1.display();
    }
}

Output

Most fruits turn yellow when ripe !
Oranges turn yellow when ripe !

In the example above the display() method in the Oranges class overrides the method in the superclass. However, using distinct objects for each class we have called both methods.
Here since the method that is called is determined when the program is being executed, this is referred to as Run-time polymorphism.

Operator Overloading.

In java and most programming languages operators such as the + operator can be overloaded. For instance, when the addition operator is used with numbers it is used to perform an arithmetic operation. However, when the same operator is used with String it is intended to perform concatenation.

Code

int num1  = 12;
int num2 = 14;
int sum = num1 + num2;

    //output = 26

However, when the same operator is used with String it is intended to perform concatenation.

Code
String firstname = 'Isaac';
String lastname = 'Tonyloi';
String fullname = firstname + lastname;
//output = Isaac Tonyloi

Connect with Isaac Tonyloi.