Java map, key = class, value = instance of that class

Question

I\'m not sure what I want to do is possible, but if it is, I want to find out how. Basically, I want to create a Map where the key is a class (java.lang.Class),

Answer 1

What you are using is a heterogeneous container. These can be made typesafe by using type tokens (as you already do) and Class.cast() with the correct application logic: So there is an unchecked suppressWarning within Class.cast(), but the application logic guarantees correctness.

I advise you read Josh Bloch's Effective Java Item 29: Consider typesafe heterogeneous containers. His example is:

// Typesafe heterogeneous container pattern - implementation
public class Favorites {
  private Map, Object> favorites =
    new HashMap, Object>();

  public  void putFavorite(Class type, T instance) {
    if (type == null)
      throw new NullPointerException("Type is null");
    favorites.put(type, instance);
  }

  public  T getFavorite(Class type) {
    return type.cast(favorites.get(type));
  }
}

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I only see a possibility for memory leakage if you hold arbitrarily many different types you actually no longer need.