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Should we @Override an interface's method implementation?

Posted by: admin November 2, 2017 Leave a comment

Questions:

Should a method that implements an interface method be annotated with @Override?

The javadoc of the Override annotation says:

Indicates that a method declaration is intended to override a method declaration in a superclass. If a method is annotated with this annotation type but does not override a superclass method, compilers are required to generate an error message.

I don’t think that an interface is technically a superclass. Or is it?

Question Elaboration

Answers:

You should use @Override whenever possible. It prevents simple mistakes from being made. Example:

class C {
    @Override
    public boolean equals(SomeClass obj){
        // code ...
    }
}

This doesn’t compile because it doesn’t properly override public boolean equals(Object obj).

The same will go for methods that implement an interface (1.6 and above only) or override a Super class’s method.

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I believe that javac behaviour has changed – with 1.5 it prohibited the annotation, with 1.6 it doesn’t. The annotation provides an extra compile-time check, so if you’re using 1.6 I’d go for it.

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You should always annotate methods with @Override if it’s available.

In JDK 5 this means overriding methods of superclasses, in JDK 6, and 7 it means overriding methods of superclasses, and implementing methods of interfaces. The reason, as mentioned previously, is it allows the compilor to catch errors where you think you are overriding (or implementing) a method, but are actually defining a new method (different signature).

The equals(Object) vs. equals(YourObject) example is a standard case in point, but the same argument can be made for interface implementations.

I’d imagine the reason it’s not mandatory to annotate implementing methods of interfaces is that JDK 5 flagged this as a compile error. If JDK 6 made this annotation mandatory, it would break backwards compatibility.

I am not an Eclipse user, but in other IDEs (IntelliJ), the @Override annotation is only added when implementing interface methods if the project is set as a JDK 6+ project. I would imagine that Eclipse is similar.

However, I would have prefer to see a different annotation for this usage, maybe an @Implements annotation.

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I would use it at every opportunity. See When do you use Java’s @Override annotation and why?

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JDK 5.0 does not allow you to use @Override annotation if you are implementing method declared in interface (its compilation error), but JDK 6.0 allows it. So may be you can configure your project preference according to your requirement.

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Overriding your own methods inherited from your own classes will typically not break on refactorings using an ide. But if you override a method inherited from a library it is recommended to use it. If you dont, you will often get no error on a later library change, but a well hidden bug.

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It’s not a problem with JDK. In Eclipse Helios, it allows the @Override annotation for implemented interface methods, whichever JDK 5 or 6. As for Eclipse Galileo, the @Override annotation is not allowed, whichever JDK 5 or 6.

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For me, often times this is the only reason some code requires Java 6 to compile. Not sure if it’s worth it.

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If a concrete class is not overriding an abstract method, using @Override for implementation is an open matter since the compiler will invariably warn you of any unimplemented methods. In these cases, an argument can be made that it detracts from readability — it is more things to read on your code and, to a lesser degree, it is called @Override and not @Implement.

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The problem with including the @Override is that it makes you think that you forgot to call the super.theOverridenMethod() method, which is very confusing. This should be crystal-clear. Perhaps Java should offer an @Interface to be used here. Oh well, yet another half-assed Java peculiarity…

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Eclipse itself will add the @Override annotation when you tell it to “generate unimplemented methods” during creation of a class that implements an interface.

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In java 6 and later versions, you can use @Override for a method implementing an interface.

But, I donot think it make sense: override means you hava a method in the super class, and you are implementing it in the sub class.

If you are implementing an interface, I think we should use @Implement or something else, but not the @Override.