Extract Generic types from extended Generic
generics, java
Solution
The problem is that `K` and `V` aren't really "repeated", at least not any more than a variable declaration and a use of that same variable are "repetition".
The way to think of this is that you declare the generic types `K` and `V`, and then you use those declared generic types in the definition of the generic type `M`. So, you don't declare the generic type `K` or `V` more than once: Rather, you declare each of them once and then refer to them in a declaration of something else.
To look at it another way, the number of generic types here is still three, namely `K`, `V`, and `M`. `M` happens to be defined in terms of `K` and `V`, but you didn't have to define `M` that way.
I should add that if you are a proponent of type inference, you might view the declaration and the use of the same variable as unnecessary repetition. However, if you're accustomed to programming in Java (or C, or C++, or many, many other languages), then you're probably accustomed to declaring variables before you use them.
Problem
I'm trying to refactor a class and set of subclasses where the M type does extend anything, even though we know it has to be a subclass of a certain type. That type is parametrized and I would like its parametrized types to be available to subclasses that already have values for M. Is there any way to define this class without having to include the redundant K and V generic types in the parameter list. I'd like to be able to have the compiler infer them from whatever M is mapped to by subclasses. ``` public abstract class NewParametrized<K, V, M extends SomeParametrized<K, V>> { public void someMethodThatTakesKAndV(K k1, V v1) { } } ``` In other words, I'd like the class declaration to look something like: ``` public class NewParametrized<M extends SomeParametrized<K, V>> { ``` And K and V's types would be inferred from the definition of M.