What's "@Override" there for in java?

Question

public class Animal {
   public void eat() { System.out.println("I eat like a generic Animal."); }

}

public class Wolf extends Animal {
   @Override
   public void eat() { System.out.println("I eat like a wolf!"); }
}

Does @Override actually have some functionality or it's just kinda comment?

Answer 1

From the Java Tutorials on annotations:

@Override — the @Override annotation informs the compiler that the element is meant to override an element declared in a superclass (overriding methods will be discussed in the the lesson titled "Interfaces and Inheritance").

   // mark method as a superclass method
   // that has been overridden
   @Override 
   int overriddenMethod() { }

While it's not required to use this annotation when overriding a method, it helps to prevent errors. If a method marked with @Override fails to correctly override a method in one of its superclasses, the compiler generates an error.

Let's take a look at the example given in the Java Language specifications, 9.6.1.4 Override. Let's say you want to override a method, equals in that case, but you wrote:

    public boolean equals(Foo that) { ... }

instead of:

    public boolean equals(Object that) { ... }

While this code is legal, annotating the equals method declaration with @Override would trigger a compile time error because you're in fact not overriding it, you're overloading it. This can cause nasty bugs and the Override annotation type helps at detecting them early.