What does @Override mean?

public cl开发者_如何学编程ass NaiveAlien extends Alien
{

    @Override
    public void harvest(){}

}

I was trying to understand my friend's code, and I do not get the syntax, @Override in the code. What does that do and why do we need in coding? Thanks.

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It's a hint for the compiler to let it know that you're overriding the method of a parent class (or interface in Java 6).

If the compiler detects that there IS no function to override, it will warn you (or error).

This is extremely useful to quickly identify typos or API changes. Say you're trying to override your parent class' method harvest() but spell it harvset(), your program will silently call the base class, and without @Override, you wouldn't have any warning about that.

Likewise, if you're using a library, and in version 2 of the library, harvest() has been modified to take an integer parameter, you would no longer override it. Again, @Override would quickly tell you.

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This feature is called an annotation. @Override is the syntax of using an annotation to let the compiler know, "hey compiler, I'm changing what harvest does in the parent class", then the compiler can immediately say, "dude, you are naming it incorrectly". The compiler won't compile until you name it correctly.

So, without this @Override annotation, the compiler won't error and it will be considered a new method declaration. It would be difficult to recognize the error at this point.

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@Override means you are overriding the base class method. In java6, it also mean you are implementing a method from an interface. It protects you from typos when you think are overriding a method but you mistyped something.