Java Generics: non-static type variable T cannot be referenced from a static context

Question

interface A {

    interface B {
       // Results in non-static type variable T cannot
       // be referenced from a static context
       T foo(); 
    }         


        

Answer 1

All member fields of an interface are by default public, static and final.

Since inner interface is static by default, you can't refer to T from static fields or methods.

Because T is actually associated with an instance of a class, if it were associated with a static field or method which is associated with class then it wouldn't make any sense

Answer 2

How about something like this.

public interface A<T> {

     interface B<T> extends A<T>{

       T foo(); 
    }

}

Answer 3

Your inner interface doesn't know what T is. Try this.

interface A<T> {

    interface B<T> {
       T foo(); 
    }

}