meaning of RuntimeException("Stub!") in Android

Alex Mawashi :

I was surfing in Android code because I wanted to see what is into Activity.finish() method.

I just wanted to have the confirmation that in Activity.finish() there would be a call to onDestroy() method.

But what I found in this method (and in many others) was:

public void finish() {
    throw new RuntimeException("Stub!");
}

So WHERE Can I find the code that really destroys the Activity? Thanks!