Polymorphism in Java

In this article, we are going to discuss one of the most powerful features of OOPs concepts Polymorphism, and we will also discuss their types and features with programming examples.

What is Polymorphism in java?

Polymorphism is one of the OOPs features, it allows us to perform a single action in different ways.

Polymorphism word comes from 2 Greek words poly and morphs, Poly means many and morphs means forms. That’s why can say polymorphism means many forms.

public class Employee{
   public void test(){
      System.out.println("Animal is making a sound");   
   }
}

public class Office extends Employee{
    @Override
    public void going(){
        System.out.println("Going to Office");
    }
}

public class Market extends Employee {
	@Override
	public void going() {
		System.out.println("Gogin to Market");
	}
}

In the above example with the same method name, we are performing different actions. As you can see that although we had the same action for all subclasses going() but there were different ways to do the same action.

This is a perfect example of polymorphism (a feature that allows us to perform a single action in different ways. It would not make any sense to just call the generic going() method as each Employee has a different going different location.

Types of polymorphism in Java.

There are two types of polymorphism in Java.

Compile-time polymorphism
Runtime polymorphism

Compile-time polymorphism.

It is also known as static polymorphism, we can achieve it using method overloading

If a class has multiple methods with having the same name but parameters are different or parameters type are different, it is known as Method Overloading.

we can overload the method in two ways

By changing the number of arguments
By changing the data type

Note: Method Overloading is not possible by changing the return type of the method only in Java.

Method Overloading Example: By using different types of arguments

// Java program for Method overloading 
  
package practice.Number;

class AdditionExample {

	// Method with 2 parameter
	static int add(int a, int b) {
		return a + b;
	}

	// Method with the same name but 2 double parameter
	static double add(double a, double b) {
		return a + b;
	}
}

package practice.Number;

class Addition {
	public static void main(String[] args) {
		System.out.println(AdditionExample.add(5, 10));

		System.out.println(AdditionExample.add(5.5, 10.5));
	}
}

Output:

15
16.0

In the above example, we are calling two add() method with different types of arguments, first calling with two int types of arguments, and in second method we are calling with two double types of arguments with the same add() method.

we notice that we are calling two methods with same name (add) but and the same number of arguments but the data types of arguments are different.

Method Overloading Example: By using different numbers of arguments.

// Java program for Method overloading 
package practice.Number;

class AdditionExample {

	// Method with 2 parameter
	static int add(int a, int b) {
		return a + b;
	}

	// Method with the same name but 3 parameter
	static int add(int a, int b, int c) {
		return a + b + c;
	}
}

package practice.Number;

class Addition {
	public static void main(String[] args) {
		System.out.println(AdditionExample.add(5, 10));

		System.out.println(AdditionExample.add(5, 10, 20));
	}
}

Output:

15
35

In the above example, we are calling two add() method with the same type of arguments but no arguments are different. In the first method, we called with two int types of arguments, and in the second method, we are calling with three int types of arguments with the same name add() method.

we notice that we are calling two methods with the same name(add) and the same type of arguments but a number of arguments are different.

Why Method Overloading is not possible by changing the return type of method only?

It is not possible because of ambiguity. When you are calling two methods with same name, same number of arguments and same type of arguments
and only the return type is different. than java not able determine to which method need to call that why we are getting ambiguity.

Let’s see how ambiguity may occur in programming:

class AdditionExample {

	// Method with 2 parameter
	static int add(int a, int b) {
		return a + b;
	}

	// Method with the same name but 2 parameter
	static double add(int a, int b) {
		return a + b;
	}
}

class Addition {
	public static void main(String[] args) {
		System.out.println(AdditionExample.add(5, 10));
	}
}

Output:

Compile Time Error: method add(int,int) is already defined in class AdditionExample

Can we overload java main() method?

Yes, we can overload main() method many times but JVM always looking for “public static void main(String[] args)” this full syntax with public static void main with string array as arguments only.

Let’s see how overload java main() method in programming:

package practice.Number;

class OverloadMain {
	public static void main() {
		System.out.println("main without args");
	}

	public static void main(String[] args) {
		System.out.println("main with String[] args");
	}

	public static void main(String args) {
		System.out.println("main with String args");
	}
}

Output:

main with String[] args

Runtime polymorphism

It is also known as Dynamic Method Dispatch, we can achieved it using method Overriding, If parent class and subClass (child class) has same method name, same argument type and same number of argument are declared. than that method is called Method Overloading.

What are the uses of Java Method Overriding?

It is used to provide the specific implementation of a method that is already provided by its ParentClass.
Method overriding is used for runtime polymorphism.

Example of without Method overriding:

//Creating a parent class.  
class Animal {
//defining a method  
	void run() {
		System.out.println("Animal is running");
	}
}

//Creating a child class  
class Dog extends Animal {
//defining the same method as in the parent class
	public static void main(String args[]) {
		Dog obj = new Dog();// creating object
		obj.run();// calling method
	}
}

Output:

Animal is running

In the above example if we are not the implementation of run() method in a subclass, and calling method through subclass object then it is automatically called the parent class run() method that why we need Method overriding.

Example of with Method overriding:

//Creating a parent class.  
class Animal {
//defining a method  
	void run() {
		System.out.println("Animal is running");
	}
}

//Creating a child class  
class Dog extends Animal {
//defining the same method as in the parent class
	void run() {
		System.out.println("Dog is running");
	}

	public static void main(String args[]) {
		Dog obj = new Dog();// creating object
		obj.run();// calling method
	}
}

Output:

Dog is running

In the above example if we are the implementation of run() method in both class subclass and parent. when we are calling run() method through subclass object then it is called the subclass class method implementation this is called Method overriding.

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Hope this was helpful for you. If you have any questions please feel free to leave a comment. Thank you for reading.

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