Question about @Override annotation

[ying lam]

Hi,

I am reading the following source code:

class secondCountDownRunner implements Runnable{
@Override
public void run() {
// ..implementation of the run method
}
}

And I have a question about @Override annotation. What does it do? Why i need to put it in my code? Isn't compiler know i am implementing the run()
of the Runnable interface?

Thank you.

[Gregg Bolinger]

It's really there as meta-data for you as the developer so when you see it you know that the marked method is actually overriding a method from the parent class. IDE's use it as well. Other than that, it does nothing. Removing the annotation has no effect as far as I know on the code.

[Campbell Ritchie]

It is really intended for overriding already implemented methods from a superclass; it is supposed to catch those annoying little spelling errors that are so hard to find when the method doesn't work. It is permitted in Java6 for methods implemented from an interface, but is redundant in that instance.

[Malcolm Storey]

Don't know about other IDE's but in Eclipse:
If the overridden method is later renamed or deleted, it causes a compile error in the overriding method. A useful safety net.
You can also change the options to make it generate a warning if @Override is not specified where it is applicable, which enforces using the safety net.

[Campbell Ritchie]

That is a nice feature about Eclipse; you can add all sorts of warnings if you use slightly un-stylish code, to maintain the code quality. I suspect other IDEs have similar warning options.