Java – multi level static nested classes produce incorrect output

When you run the following code, "x.q" instead of "a" will be printed as required by the language specification

Solution

The reason why you receive "x.q" is that x refers to an unnamed package with X scope, not a < T > 10. Declaring "external" X after B is not important because the java compiler sees B. Y's base class name before it resolves it

You can force inheritance from A. X in your code as follows:

class B extends A<B.Y.Q> {
    static class Y extends A.X {
    } //                   ^^
      //                Add this
}

Demo 1.

Editor: (thanks for user695022's comments)

Strangely, if the external class is not generic, the problem disappears:

class A {
    static class X {
        static class Q {
            public static void main() {
                System.out.println("A<T>.X.Q");
            }
        }
    }
}

Demo 2.