Java – Final arguments in interface methods – what’s the point

classfinalinterfacejavamethods

In Java, it is perfectly legal to define final arguments in interface methods and do not obey that in the implementing class, e.g.:

public interface Foo {
    public void foo(int bar, final int baz);
}

public class FooImpl implements Foo {

    @Override
    public void foo(final int bar, int baz) {
        ...
    }
}

In the above example, bar and baz has the opposite final definitions in the class VS the interface.

In the same fashion, no final restrictions are enforced when one class method extends another, either abstract or not.

While final has some practical value inside the class method body, is there any point specifying final for interface method parameters?

Best Answer

It doesn't seem like there's any point to it. According to the Java Language Specification 4.12.4:

Declaring a variable final can serve as useful documentation that its value will not change and can help avoid programming errors.

However, a final modifier on a method parameter is not mentioned in the rules for matching signatures of overridden methods, and it has no effect on the caller, only within the body of an implementation. Also, as noted by Robin in a comment, the final modifier on a method parameter has no effect on the generated byte code. (This is not true for other uses of final.)

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