Method overriding in Java

 

✅ What is Method Overriding in Java?

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

The overridden method in the subclass should have:

• Same method name

• Same return type (or subtype - called covariant return type)

• Same parameter list

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🧠 Purpose of Overriding

To implement runtime polymorphism, where the method that gets called depends on the object's runtime type, not the reference type.

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📘 Example of Method Overriding

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

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

public class Main {
    public static void main(String[] args) {
        Animal a = new Dog();  // Upcasting
        a.sound();  // Calls Dog's overridden method
    }
}

🧾 Output:

Dog barks

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🔎 Key Points about Method Overriding

Rule / Feature	Description
Same Signature	Name and parameters must be identical
Access Modifier	Can’t be more restrictive than the superclass method
Return Type	Must be the same or a subtype (covariant)
@Override Annotation	Optional but recommended – helps catch errors
Static/Private/Final Methods	Cannot be overridden
Constructors	Cannot be overridden

🔐 Access Modifier Example

class Parent {
    protected void show() {
        System.out.println("Parent class");
    }
}

class Child extends Parent {
    // Must be same or more visible (protected or public)
    @Override
    public void show() {
        System.out.println("Child class");
    }
}

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❌ Invalid Overriding Example (Compile-time Error)

class Parent {
    private void show() {
        System.out.println("Parent");
    }
}

class Child extends Parent {
    @Override
    void show() {  // ❌ Cannot override private method
        System.out.println("Child");
    }
}

Explanation: show() in Parent is private – not visible to Child.

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🆚 Method Overloading vs Method Overriding

Feature	Method Overloading	Method Overriding
Occurs in	Same class	Between superclass and subclass
Parameters	Must differ	Must be the same
Return Type	Can differ	Must be same or subtype
Access Modifier	Any	Cannot be more restrictive
Polymorphism Type	Compile-time	Runtime

🧪 Real-world Analogy

Think of a base class Printer that prints documents. A ColorPrinter (subclass) can override the method to print in color, while BlackAndWhitePrinter prints in black-and-white – same method, different behavior.