Polymorphism

Poly means many, morph means forms. Polymorphism means the same method name can perform different behaviours.

• Same method name.
• Different behaviour depending on the object or the inputs.

Real World Example: Employee

Different employees perform work() differently.

• Employee: work()
• Developer: work() → Write Code
• Designer: work() → Create Designs

Same method: work(). Different behaviour for each employee type.

Method Overriding

Child class gives its own behaviour for an inherited method, this is called overriding.

class Employee {
    public void work() {
        System.out.println("Working...");
    }
}

class Developer extends Employee {
    @Override
    public void work() {
        System.out.println("Writing code");
    }
}

Developer keeps the same work() name as Employee but replaces what it does.

• Same method: work()
• Different behaviour: Writing code

Method Overloading

Same method name with different parameters, this is called overloading.

class Employee {
    public void work() {
        System.out.println("Working...");
    }

    public void work(int hours) {
        System.out.println("Working " + hours + " hours");
    }
}

Java picks the right version of work() based on what arguments are passed in.

• work()
• work(5)
• Same method name, different inputs.

Class Diagram

┌─────────────────────────┐
│        Employee         │
├─────────────────────────┤
│ +work(): void           │
│ +work(int): void        │
└─────────────────────────┘
             ▲
             │ extends
┌─────────────────────────┐
│        Developer        │
├─────────────────────────┤
│ +work(): void           │
└─────────────────────────┘

Employee shows overloading (work() and work(int) side by side). Developer extending Employee and replacing work() shows overriding.

Exam Focus Points

• Polymorphism lets one method name behave differently depending on the object or the arguments used.
• Overloading happens in the same class: same name, different parameter lists.
• Overriding happens between parent and child classes: same name and parameters, different implementation, using @Override.

Summary

• Polymorphism means one method name can take many forms.
• Method overloading defines multiple versions of a method in the same class, distinguished by their parameters.
• Method overriding lets a child class replace a method it inherited from its parent class.
• Polymorphism = One Name, Many Forms.