Should a method that implements an interface method be annotated with @Override?

Yes, it is recommended to annotate a method that implements an interface method with @Override in Java. While it is not strictly required (the code will still compile and run without it), using @Override has several advantages that improve code readability, maintainability, and correctness.

Why You Should Use @Override for Interface Methods

1. Enforces Correct Implementation

When you use @Override, the compiler checks that the method correctly implements a method declared in the interface. If there is a mismatch in the method signature (e.g., a typo in the method name or parameter list), the compiler will generate an error.

Example:

interface Animal {
    void speak();
}

class Dog implements Animal {
    @Override
    public void speak() { // Compiler verifies this overrides Animal.speak()
        System.out.println("Bark!");
    }
}

If you mistakenly write the method with a typo:

class Dog implements Animal {
    @Override
    public void speek() { // Compiler error: Method does not override or implement a method from a supertype
        System.out.println("Bark!");
    }
}

Without @Override, this error would go unnoticed, leading to a bug.

2. Improves Code Readability

The @Override annotation explicitly indicates that the method is overriding or implementing a method from a superclass or interface. This makes the code more readable and understandable to other developers.

3. Protects Against Interface Changes

If the interface definition changes (e.g., the method signature is updated), methods marked with @Override will cause a compilation error, alerting you to fix the implementation.

Example:

interface Animal {
    void speak(String language);
}

// Existing implementation
class Dog implements Animal {
    @Override
    public void speak() { // Compilation error: Method no longer matches the interface
        System.out.println("Bark!");
    }
}

Without @Override, the mismatch would not cause an error, and the code would silently fail to implement the updated interface correctly.

4. Avoids Mistakes with Superclass and Interface Confusion

If a class extends a superclass and implements an interface, @Override ensures that you’re overriding the intended method and not accidentally creating a new method.

Example:

interface Animal {
    void speak();
}

class Mammal {
    void speak() {
        System.out.println("Generic mammal sound");
    }
}

class Dog extends Mammal implements Animal {
    @Override
    public void speak() { // Ensures this implements Animal.speak(), not overriding Mammal.speak()
        System.out.println("Bark!");
    }
}

Is @Override Mandatory for Interface Methods?

• Pre-Java 6: The @Override annotation was only applicable to methods overriding a superclass method. Using it for interface methods caused a compilation error.
• Java 6 and Later: The @Override annotation can (and should) be used for methods implementing an interface method.

Best Practice

Always use @Override for methods that implement interface methods. It ensures correctness, prevents subtle bugs, and enhances code clarity.

If you're interested in mastering object-oriented programming principles, explore Grokking Advanced Coding Patterns for Interviews or Grokking Data Structures & Algorithms for Coding Interviews on DesignGurus.io! These resources can help deepen your understanding of interface-driven design and implementation.