Does java support "Soft" interfaces?

Question

Consider the following scenario: Say that you created an interface Foo:

public interface Foo {

    public void bar();

}

And say that there is an old class SomeOldClass in a certain library that you want to use. It already has the bar() method, but does not explicitly implement Foo.

You have written the following code for all classed that implement Foo:

public <T extends Foo> T callBarOnThird(List<T> fooList){
    return fooList.get(2).bar();
}

And now you want it to also work for SomeOldClass. You dont have access to the source code of this class, so you can't modify it.

Is there a way to declare Foo or something similar as some sort of "soft" interface, (as in where any class that implements all the required methods would be accepted as an implicit implementation of the soft interface)? If not, how would you solve this with code that is as clean as possible?

Answer 1

No, it does not.

You have to provide an adapter instance (there are several methods and tools to help with that, but Java does not do it "implicitly").