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Polymorphism Java Example (with video)

In this post, we feature a comprehensive Polymorphism Java Example.

1. Introduction

In word Polymorphism, the word Poly stands for ‘many’ and the word morph stands for ‘forms’. Polymorphism is the ability of an object to take on many forms. Polymorphism is the capability of an action or method to do different things based on the object that it is an action upon. Polymorphism is one of the Object-Oriented Programming principles used along with Encapsulation and Inheritance in Programming languages like C++, Java, and Python. It provides flexibility to the programmers to interact with different objects by using the same message.

You can also check this tutorial in the following video:

Java Polymorphism Tutorial – video

2. Types of Polymorphism

In Java, Polymorphism can be achieved in two ways using Method Overloading and Method Overriding. Method Overloading is also called as Compile time Polymorphism or early binding, whereas Method Overriding is also called as Runtime Polymorphism or late binding. Let us now understand in detail both of them.

polymorphism java

2.1 Method Overloading

Two methods are said to overloaded if they have the same method name and different parameters i.e either two methods should have a different number of parameters or the data types of the parameters of two methods must be different.

Let us understand this with a coding snippet below:

// program to show method overloading in java
package com.javacodegeeks.snippets.core;

class Example1
{
	public static String add(String s1, String s2) //method to perform String concatenation
	{
		return s1+s2;
	}

	public static int add(int a,int b)  //method to perform int addition
	{
		return a+b;
	}
	public static void main(String[] args) {
		
		System.out.println(add(10,30));  //calls add function with int params
		System.out.println(add("Rajesh","Kumar")); //calls add function with String params
	}
}
Output
40
RajeshKumar

In this example, when we pass String parameters to the method add, add() method at Line 6 is getting executed. This method returns the String after concatenation of both Strings s1 and s2. But when we passed integer values to the add method, add() method at Line 11 is getting executed and it returns the addition of two values. Here we used the same method name add, we are able to interact with two functionalities based on the parameters which are passed.

The compiler is able to recognize these method calls and therefore it is also called Compile time Polymorphism.

2.2 Method Overriding

In Method Overriding, during Inheritance, a child class provides its own implementation to the Parent’s method, thereby overriding the implementation of the parent. Two methods are said to be overridden only if they have the same Signature, that is, the same name and same parameters.

In this context, the Parent’s method is called an Overridden method and the Child’s method is called an Overriding method.

Let us understand what does below coding snippet contains :

  • Shape class has two methods, drawShape() and eraseShape().
  • Classes Circle, Square and Triangle extend Shape and override its two methods, each one in a different way.
  • RandomShapeGenerator class has a method, Shape next() that randomly creates one of the above classes, Circle, Square and Triangle.
  • We create a new RandomShapeGenerator instance and a new Shape array.
  • We fill the Shape array, by creating random shapes, using the next() method of RandomShapeGenerator.
  • Then we call drawShape() method, so each time the method of the object created randomly is called.

Let us take a look at the code snippet that follows:  

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package com.javacodegeeks.snippets.core;
 
import java.util.Random;
 
class Shape {
 
    void drawShape() {
    }
 
    void eraseShape() {
    }
}
 
class Circle extends Shape {
 
    @Override
    void drawShape() {
 
  System.out.println("Circle.draw()");
    }
 
    @Override
    void eraseShape() {
 
  System.out.println("Circle.erase()");
    }
}
 
class Square extends Shape {
 
    @Override
    void drawShape() {
 
  System.out.println("Square.draw()");
    }
 
    @Override
    void eraseShape() {
 
  System.out.println("Square.erase()");
    }
}
 
class Triangle extends Shape {
 
    @Override
    void drawShape() {
 
  System.out.println("Triangle.draw()");
    }
 
    @Override
    void eraseShape() {
 
  System.out.println("Triangle.erase()");
    }
}
 
// A "factory" that randomly creates shapes:
class RandomShapeGenerator {
 
    private Random rand = new Random();
      
    //Choose randomly a circle, a squere or a triangle
    public Shape next() {
 
  switch (rand.nextInt(3)) {
 
 
default:
 
 
case 0:
 
 
    return new Circle();
 
 
case 1:
 
 
    return new Square();
 
 
case 2:
 
 
    return new Triangle();
 
  }
    }
}
 
public class Polymorphism {
    
    private static RandomShapeGenerator gen = new RandomShapeGenerator();
 
    public static void main(String[] args) {
 
   
 
  //This is an array of references of the superclass Shape
 
  Shape[] s = new Shape[9];
 
   
 
  // Fill up the array with random shapes shapes:
 
  for (int i = 0; i < s.length; i++) {
 
 
s[i] = gen.next();
 
  }
 
   
 
  //s[x].drawShape will call the specific drawShape function of whichever
 
  //shape is s[x] and not the drawShape function of class Shape
 
  //That's polymorphism.
 
  for (int i = 0; i < s.length; i++) {
 
 
s[i].drawShape();
 
  }
 
    }
}
Output
Square.draw()
Square.draw()
Circle.draw()
Triangle.draw()
Triangle.draw()
Square.draw()
Circle.draw()
Circle.draw()
Square.draw()

3. Benefits of Polymorphism

1. Method overloading allows methods that perform similar or closely related functions to be accessed through a common name. For example, a program performs operations on an array of numbers which can be int, float, or double type. Method overloading allows you to define three methods with the same name and different types of parameters to handle the array operations.

2. Method overloading can be implemented on constructors allowing different ways to initialize objects of a class. This enables you to define multiple constructors for handling different types of initializations.

3. Method overriding allows a subclass to use all the general definitions that a superclass provides and adds specialized definitions through overridden methods.

4. Method overriding works together with inheritance to enable code-reuse of existing classes without the need for re-compilation.

4. Polymorphism Java Example

In this post, we have started with Polymorphism definition, how it can be achieved in Java using Method Overloading and Method Overriding. Then we clearly understood how we can implement Method Overloading and Method Overriding programmatically. Finally, we ended our topic by understanding the benefits of using Polymorphism.

6. Download the Source Code

This is an example of Polymorphism in java.

Download
You can download the full source code of this example here: Polymorphism Java Example

Last updated on May 22nd, 2021

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