Question

public Interface Foo<T extends Colors>{...}

Is there a way to retrieve which T was given for an implementation of Foo?

For example,

public Class FooImpl implements Foo<Green>{..}

Would return Green.

Answer 1

Contrary to other answers, you can obtain the type of a generic parameter. For example, adding this to a method inside a generic class will obtain the first generic parameter of the class (T in your case):

ParameterizedType type = (ParameterizedType) getClass().getGenericSuperclass();
type.getActualTypeArguments()[0]

I use this technique in a generic Hibernate DAO I wrote so I can obtain the actual class being persisted because it is needed by Hibernate. It works!