Consider the example:
package testImplementDefaultMethodHint;

public class ImplementDefaultMethodHint {

    I i = new I() {

    }
}

interface I {
    void x();
    void y();
    default void z() {}
}


1) Notice the hint offered on line where new instance of anonymous class is created.
2) When hint "Implement all abstract methods" is applied it does not add the method z()

I understand that z() in fact is not an abstract method. So technically this is maybe correct.

But what if I (ab)used default modifier to make an API compatible change in the interface I which had existed a long time before method z() was added? The default method is then the only possibility I had. And in this situation it is a method that I want to be implemented by classes that implement interface I.

How many other possibilities there are to find out that method z() can be implemented? Luckily there is code completion. But Generate Override Methods does not offer z(). Let's imagine that there are no sources for interface I available. Not easy situation to implement interface I properly, do you agree?