Polymorphism in Java with Example

Introduction

Polymorphism is one of the core concepts of Object-Oriented Programming (OOP). It allows methods to do different things based on the object it is acting upon, even though they share the same name. Polymorphism provides a way to perform a single action in different forms. In Java, polymorphism can be achieved through method overloading and method overriding.

Table of Contents

1. What is Polymorphism?
2. Types of Polymorphism
3. Method Overloading
4. Method Overriding
5. Real-World Examples of Polymorphism
6. Example: Polymorphism with Method Overloading
7. Example: Polymorphism with Method Overriding
8. Example: Payment Processing Example
9. Conclusion

1. What is Polymorphism?

Polymorphism means "many shapes" or "many forms." In Java, it refers to the ability of a single method or class to take on multiple forms. This is achieved through method overloading (compile-time polymorphism) and method overriding (runtime polymorphism).

2. Types of Polymorphism

• Compile-time Polymorphism (Method Overloading): This type of polymorphism is resolved during compile time. Method overloading allows a class to have more than one method with the same name, provided their parameter lists are different.
• Runtime Polymorphism (Method Overriding): This type of polymorphism is resolved during runtime. Method overriding allows a subclass to provide a specific implementation of a method that is already defined in its superclass.

3. Method Overloading

Method overloading occurs when a class has multiple methods with the same name but different parameter lists (different types or numbers of parameters).

Example:

public class MathUtils {
    public int add(int a, int b) {
        return a + b;
    }

    public double add(double a, double b) {
        return a + b;
    }

    public int add(int a, int b, int c) {
        return a + b + c;
    }
}

4. Method Overriding

Method overriding occurs when a subclass provides a specific implementation of a method that is already defined in its superclass.

Example:

class Animal {
    public void makeSound() {
        System.out.println("Animal makes a sound");
    }
}

class Dog extends Animal {
    @Override
    public void makeSound() {
        System.out.println("Dog barks");
    }
}

class Cat extends Animal {
    @Override
    public void makeSound() {
        System.out.println("Cat meows");
    }
}

5. Real-World Examples of Polymorphism

Example 1: Different Behaviors of a Person

Suppose you are in a classroom, you behave like a student. When you are in the market, you behave like a customer. When you are at home, you behave like a son or daughter. Here, one person exhibits different behaviors in different contexts.

Example 2: Payment Processing System

In a payment processing system, different payment methods such as credit card, debit card, and PayPal have different processing steps.

6. Example: Polymorphism with Method Overloading

Example:

public class Printer {
    public void print(String message) {
        System.out.println(message);
    }

    public void print(int number) {
        System.out.println(number);
    }

    public void print(double number) {
        System.out.println(number);
    }

    public static void main(String[] args) {
        Printer printer = new Printer();
        printer.print("Hello, World!");  // Output: Hello, World!
        printer.print(123);             // Output: 123
        printer.print(3.14);            // Output: 3.14
    }
}

Explanation:

• Printer: Class with overloaded print methods to handle different types of input.
• Main method: Demonstrates the use of overloaded print methods.

7. Example: Polymorphism with Method Overriding

Example:

class Animal {
    public void makeSound() {
        System.out.println("Animal makes a sound");
    }
}

class Dog extends Animal {
    @Override
    public void makeSound() {
        System.out.println("Dog barks");
    }
}

class Cat extends Animal {
    @Override
    public void makeSound() {
        System.out.println("Cat meows");
    }
}

public class Main {
    public static void main(String[] args) {
        Animal myDog = new Dog();
        Animal myCat = new Cat();

        myDog.makeSound();  // Output: Dog barks
        myCat.makeSound();  // Output: Cat meows
    }
}

Explanation:

• Animal: Base class with a makeSound method.
• Dog and Cat: Subclasses that override the makeSound method.
• Main method: Demonstrates runtime polymorphism by calling the overridden methods on Dog and Cat objects.

8. Example: Payment Processing Example

Class Diagram

Code Example:

Payment Interface:

interface Payment {
    void pay();
}

CashPayment Class:

class CashPayment implements Payment {
    @Override
    public void pay() {
        System.out.println("Payment made using cash.");
    }
}

CreditPayment Class:

class CreditPayment implements Payment {
    @Override
    public void pay() {
        System.out.println("Payment made using credit card.");
    }
}

Client Class:

public class Polymorphism {
    public static void main(String[] args) {
        Payment payment;

        payment = new CashPayment();
        payment.pay();  // Output: Payment made using cash.

        payment = new CreditPayment();
        payment.pay();  // Output: Payment made using credit card.
    }
}

Explanation:

• Payment: Interface defining the pay method.
• CashPayment and CreditPayment: Classes implementing the Payment interface and providing their own implementations of the pay method.
• Polymorphism: Client class demonstrating polymorphism by using the Payment interface to call the pay method on different types of payment objects.

9. Conclusion

Polymorphism in Java is a powerful concept that allows methods to perform different tasks based on the object they are acting upon. It enhances flexibility and maintainability in code by allowing a single method or class to take on multiple forms. Method overloading and method overriding are two ways to achieve polymorphism in Java. Real-world examples like different behaviors of a person in different contexts and various payment processing methods further illustrate the usefulness of polymorphism.

Happy coding!