Polymorphism in Java

Polymorphism in Java

What is Polymorphism?

Polymorphism means “many forms.” In Java, it allows an object to take multiple forms. It is one of the four main OOP (Object-Oriented Programming) concepts, along with inheritance, encapsulation, and abstraction.

Polymorphism in Java occurs in two main types:

  1. Compile-time Polymorphism (Method Overloading)
    • Happens at compile time.
    • Achieved by method overloading (same method name, different parameters).
  2. Run-time Polymorphism (Method Overriding)
    • Happens at runtime.
    • Achieved by method overriding (subclass provides a specific implementation of a method already defined in the parent class).

Example of Compile-time Polymorphism (Method Overloading)

class Calculator {
    // Add two integers
    int add(int a, int b) {
        return a + b;
    }

    // Add three integers
    int add(int a, int b, int c) {
        return a + b + c;
    }
}

public class Main {
    public static void main(String[] args) {
        Calculator calc = new Calculator();
        System.out.println(calc.add(5, 10));       // Output: 15
        System.out.println(calc.add(5, 10, 15));   // Output: 30
    }
}

✅ Here, the add method behaves differently depending on the number of arguments.

Example of Run-time Polymorphism (Method Overriding)

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

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

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

public class Main {
    public static void main(String[] args) {
        Animal myAnimal;

        myAnimal = new Dog();
        myAnimal.sound();  // Output: Dog barks

        myAnimal = new Cat();
        myAnimal.sound();  // Output: Cat meows
    }
}

✅ Here, the same reference type (Animal) behaves differently depending on the object it refers to at runtime. This is runtime polymorphism.

Key Points

  • Polymorphism improves code flexibility and reusability.
  • Compile-time polymorphism → Method overloading
  • Run-time polymorphism → Method overriding
  • Achieved mainly through inheritance and interfaces.

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