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

public class Animal {
   public void eat() { System.out.println("I eat like a generic Animal.");开发者_如何转开发 }

}

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?

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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.

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Override annotation is a compile time annotation which makes java compiler throw an error if the method having this annotation is actually not overriding a parent class method. You can try to change the Wolf class to not extend the Animal class and if Override annotation is present it will show you a compile time error

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something like it alerts at compile time by throwing compilation error if you are not really overriding the method. similar Q here-When do you use Java's @Override annotation and why?

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It works as a comment, but also as an assertion that you actually ARE overriding something. If you use @Override, but it does not actually override anything, the compiler will generate an error. See the documentation page for more details.

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If you remove the "eat" method from the parent class or misspell it as "eats" in the subclass, your code will now fail to compile. Without the "@Override" annotation, you can do either and your code will still compile, it just won't do what you want (namely, override a method).

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It does not do anything at run-time, but it helps you to catch errors:

If you thought you would override a method, but do not (because of a speling problem or parameter types), without the annotation, the code would compile to something useless (as in: your method would not be called, but the superclass method that you accidentally did not override gets called).