🟣 OOP · Lesson 20

Polymorphism

Written and reviewed by Gagan Bhardwaj · Senior IT Faculty · 15+ years’ experience

What is Polymorphism?

Polymorphism means "many forms". In Java it lets one method name behave differently depending on the object or the arguments. It is one of the four pillars of OOP and makes code flexible and extensible.

💡 Meaning

Poly = many, morph = forms. The same action (e.g. draw()) takes many forms for different shapes.

Two Types of Polymorphism

Type	Also called	How
Compile-time	Method Overloading	Same method name, different parameters — resolved by the compiler.
Runtime	Method Overriding	Child class redefines a parent method — resolved at runtime.

1) Overloading (compile-time)

Java

class Calc {
    int add(int a, int b) { return a + b; }
    double add(double a, double b) { return a + b; }  // same name, different types
}

▶ Output

add(2,3) → 5    add(2.5,1.5) → 4.0

2) Overriding (runtime)

Java

class Animal { void sound() { System.out.println("Some sound"); } }
class Cat extends Animal {
    void sound() { System.out.println("Meow"); }  // overrides parent
}
Animal a = new Cat();
a.sound();  // runtime picks Cat's version

▶ Output

Meow

Why It's Useful

Write general code (e.g. Animal a) that works for many specific types.
Add new subclasses without changing existing code.
Cleaner APIs — one method name instead of many.

⚠️ Overloading vs Overriding

Overloading = same class, different parameters (compile-time). Overriding = parent & child, same signature (runtime). Don't confuse the two.

Summary

Polymorphism = one name, many forms.
Compile-time (overloading) and runtime (overriding).
Makes code flexible, reusable and easy to extend.

Polymorphism क्या है?

Polymorphism का मतलब है "कई रूप"। Java में यह एक ही method नाम को object या arguments के हिसाब से अलग व्यवहार करने देता है। यह OOP के चार स्तंभों में से एक है और code को flexible बनाता है।

💡 मतलब

Poly = कई, morph = रूप। एक ही action (जैसे draw()) अलग-अलग shapes के लिए कई रूप लेता है।

Polymorphism के दो प्रकार

प्रकार	दूसरा नाम	कैसे
Compile-time	Method Overloading	एक ही नाम, अलग parameters — compiler तय करता है।
Runtime	Method Overriding	Child class parent method दोबारा define करे — runtime पर तय।

1) Overloading

Java

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

▶ Output

add(2,3) → 5    add(2.5,1.5) → 4.0

2) Overriding

Java

class Cat extends Animal {
    void sound() { System.out.println("Meow"); }
}
Animal a = new Cat();  a.sound();

▶ Output

Meow

क्यों उपयोगी है

General code लिखें जो कई specific types के लिए काम करे।
नई subclasses जोड़ें बिना पुराना code बदले।
साफ़ APIs — एक नाम, कई काम।

⚠️ Overloading vs Overriding

Overloading = एक ही class, अलग parameters (compile-time)। Overriding = parent और child, एक ही signature (runtime)।

सारांश

Polymorphism = एक नाम, कई रूप।
Compile-time (overloading) और runtime (overriding)।
Code को flexible, reusable और extend करने में आसान बनाता है।

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