Question

Say I have a parent interface/class like so

interface Parent<T> {}

And a number of implementing interfaces that fix the generic type.

interface Child extends Parent<Type> {}

Can I use reflection to get the instance of Class representing T if I have the Class object for Child. Something like this:

<T, I extends Parent<T>> I create(Class<I> type) {
    Class<T> tType = ...
    ...
}

Currently I’m having tType be passed in as a parameter, but I’d like to simplify things if I can.

Answer 1

Yes, despite what the others have said, this info is available if you have access to the subclass’ Class object. You need to use getGenericSuperclass along with getActualTypeArguments.

ParameterizedType superClass = (ParameterizedType)childClass.getGenericSuperclass();
System.out.println(superClass.getActualTypeArguments()[0]);

In your example, the “actual” type argument should return the Class for Type.