Method Overriding & @Override Annotation Rules

1Concept

Method Overriding allows a subclass to provide a specific implementation of a method defined in its superclass. Rules: 1. Exact same method name and parameter types; 2. Return type must be identical or a subtype (Covariant Return Type); 3. Access level cannot be more restrictive; 4. Cannot throw broader checked exceptions.

2Architecture Diagram

Superclass:  public Number calculate()  (Broader return type)
Subclass:    public Integer calculate() (Covariant subtype return: VALID!)

3Code Example

public class MethodOverridingDemo {
    static class PaymentService {
        public String processPayment(double amount) {
            return "Standard payment processed: $" + amount;
        }
    }

    static class CryptoPaymentService extends PaymentService {
        @Override
        public String processPayment(double amount) {
            return "Crypto payment processed via Blockchain: $" + amount;
        }
    }

    public static void main(String[] args) {
        PaymentService service = new CryptoPaymentService(); // Upcasting
        System.out.println(service.processPayment(250.0)); // Polymorphic dispatch
    }
}

4Expected Output

CryptoPaymentService: Crypto payment processed via Blockchain: $250.0

5Key Takeaways

• ✓Always apply `@Override` annotation; it instructs the compiler to verify matching method signatures.
• ✓Private, static, and final methods CANNOT be overridden.
• ✓Subclasses can broaden access (e.g. protected -> public), but never restrict it (e.g. public -> private).