Polymorphism in Java
Method Overloading and Overriding

In Java, polymorphism is one of the four core principles of object-oriented programming (OOP), alongside inheritance, encapsulation, and abstraction. At its core, polymorphism allows objects to take many forms depending on the context. This dynamic nature leads to more flexible and maintainable code.

There are two main types of polymorphism in Java:

• Compile-time Polymorphism (also known as method overloading)
• Runtime Polymorphism (also known as method overriding)

Why Use Polymorphism?

Polymorphism simplifies code reusability, enhances scalability, and allows us to build systems that are easier to extend and modify. Imagine writing a sorting algorithm that works on different types of objects — with polymorphism, that's not just possible, it's elegant.

1. Compile-time Polymorphism (Method Overloading)

Compile-time polymorphism occurs when multiple methods in the same class have the same name but different parameter lists. The decision about which method to call is made by the compiler.

Example: Method Overloading

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

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

    int add(int a, int b, int c) {
        return a + b + c;
    }
    
    public static void main(String[] args) {
        Calculator calc = new Calculator();
        System.out.println(calc.add(2, 3));
        System.out.println(calc.add(2.5, 3.5));
        System.out.println(calc.add(1, 2, 3));
    }
}

5
6.0
6

Explanation:

Here, the method add is overloaded three times. The compiler picks the correct version to invoke based on the number and types of arguments. This helps in writing intuitive APIs while avoiding redundant method names.

2. Runtime Polymorphism (Method Overriding)

Runtime polymorphism happens when a subclass provides a specific implementation of a method that is already defined in its superclass. The method that gets executed is determined at runtime based on the object's actual type.

Example: Method Overriding

class Animal {
    void sound() {
        System.out.println("Some generic animal sound");
    }
}

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

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

public class TestPolymorphism {
    public static void main(String[] args) {
        Animal a;
        a = new Dog();
        a.sound();

        a = new Cat();
        a.sound();
    }
}

Dog barks
Cat meows

Explanation:

Even though the reference variable a is of type Animal, the actual object it points to is either a Dog or a Cat. At runtime, Java determines the real object and invokes the appropriate sound() method. This is known as dynamic method dispatch.

Polymorphism in Action: Real-World Analogy

Imagine you have a remote control. Whether it operates a TV, a fan, or an AC depends on the device it’s currently linked to. The same remote (reference) can behave differently (method call) depending on the actual device (object instance) — this is polymorphism in everyday life.

Benefits of Using Polymorphism

• Extensibility: Add new classes without modifying existing code.
• Maintainability: Simplifies managing and debugging.
• Reusability: Write generic code that works with any subclass.

Things to Remember

• Overloading is determined at compile time, based on method signatures.
• Overriding is resolved at runtime, based on the actual object type.
• Only instance methods can be overridden, not static methods.
• Constructors cannot be overridden or overloaded in the same way.

Quick Recap

Feature	Method Overloading	Method Overriding
Type	Compile-time	Runtime
Class Involvement	Same class	Parent and child classes
Signature	Different parameter list	Same method signature
Polymorphism	Static	Dynamic

Conclusion

Java Polymorphism isn’t just a concept—it’s a paradigm shift in how we design programs. With method overloading, you get cleaner, more intuitive code. With method overriding, you get flexibility and adaptability.