What is the static type of `this` in Java 8 default interfaces?

Question

I'm implementing the visitor pattern for a project and realized I may be able to save some typing by having the default implementation of accept be the following.

public interface Visitable {
    default public void accept(Visitor v) {
        v.visit(this);
    }
}

However if the static type of this resolves to Visitable this implementation will not work so what is the static type of this in this situation?

Answer 1

Since, in your context, this is used as a parameter type, the call will be resolved to Visitor#visit(Visitable) at compile- and runtime. Thus, you gain nothing from trying to make a default method in this scenario.

The only time this can be used polymorphically is when using it as the receiver:

public interface Foo
{
    public default void bar()
    {
         this.bar(1);
    }

    public void bar(int i);
}