Remember that in Java, for a reference variable of some type referring an object of its supertype is forbidden: arrows in Figure 8 must not be directed upwards.

Pass class objects: Use Class<T> objects to retain type information at runtime. Use reflection: Java’s Reflection API allows inspection of generic types—but with some limitations.

Okay, I've got two objects. There's the Hand object, and the Finger object. These are fake. The mappings are correct, I believe, everything works fine usually, I think I'm just misunderstanding ...