When do you use Java's @Override annotation and why?

Question

What are the best practices for using Java's @Override annotation and why?

It seems like it would be overkill to mark every single overridden method with the @Override annotation. Are there certain programming situations that call for using the @Override and others that should never use the @Override?

Answer 1

Use it every time you override a method for two benefits. Do it so that you can take advantage of the compiler checking to make sure you actually are overriding a method when you think you are. This way, if you make a common mistake of misspelling a method name or not correctly matching the parameters, you will be warned that you method does not actually override as you think it does. Secondly, it makes your code easier to understand because it is more obvious when methods are overwritten.

Additionally, in Java 1.6 you can use it to mark when a method implements an interface for the same benefits. I think it would be better to have a separate annotation (like @Implements), but it's better than nothing.

Answer 2

I think it is most useful as a compile-time reminder that the intention of the method is to override a parent method. As an example:

protected boolean displaySensitiveInformation() {   return false; } 

You will often see something like the above method that overrides a method in the base class. This is an important implementation detail of this class -- we don't want sensitive information to be displayed.

Suppose this method is changed in the parent class to

protected boolean displaySensitiveInformation(Context context) {   return true; } 

This change will not cause any compile time errors or warnings - but it completely changes the intended behavior of the subclass.

To answer your question: you should use the @Override annotation if the lack of a method with the same signature in a superclass is indicative of a bug.