Generics and inheritance: need a complex Map instance

Question

public abstract class Mother {
}

public class Daughter extends Mother {
}

public class Son extends Mother {
}


        

Answer 1

I don't think it's possible to encode this in the type, I'd do it with a custom class

class ClassMap<T> {
  private Map<Class<? extends T>, List<? extends T>> backingMap = new HashMap<>();

  public <E extends T> void put(Class<E> cls, List<E> value) {
    backingMap.put(cls, value);
  }

  @SuppressWarnings("unchecked")
  public <E extends T> List<E> get(Class<E> cls) {
    return (List<E>)backingMap.get(cls);
  }
}

It's safe to suppress warnings here as long as you don't leak the backingMap reference outside this class.

Answer 2

Assuming you're looking for a single map, no this is not possible.