In Java is it possible to create a type-safe Map of classes to instances of their class?

You mean something like this ?

public class Favorites {
  private Map<Class<?>, Object> favorites =
    new HashMap<Class<?>, Object>();

  public <T> void setFavorite(Class<T> klass, T thing) {
    favorites.put(klass, thing);
  }

  public <T> T getFavorite(Class<T> klass) {
    return klass.cast(favorites.get(klass));
  }

  public static void main(String[] args) {
    Favorites f = new Favorites();
    f.setFavorite(String.class, "Java");
    f.setFavorite(Integer.class, 0xcafebabe);
    String s = f.getFavorite(String.class);
    int i = f.getFavorite(Integer.class);
  }
}

see as reference: Java map with values limited by key's type parameter

As I understand you, you're saying that after you create this map, you want to populate it with something like ...

f.put(String.class, "Hello");
f.put(Integer.class, new Integer(42));
f.put(x.getClass(), x);

etc. Right?

In that case, I think the answer is no, you cannot do that with generics. Generics say that for a given instance of the class -- the map in this case -- you are specifying the types that are applicable. So if you say new HashMap<String,Integer>;, you are saying that all operations against this map will use a key that is a string and a value that is an integer. But that's not what you want to do in this case. You want to be able to put any sort of object into the class, and then constrain the acceptable types for the key based on the type of the object. That's not how generics work. They're not a relationship between each other, they're a constant for any given instance.

You could, of course, create such a map as new HashMap<Class,Object>;. This wouldn't force the class to be the class of the corresponding object, but it would allow you to enter such values.

Besides that, I think you'd need a wrapper. Should I point out that the wrapper's put would only need one parameter, as it could presumably determine the class of the parameter by doing getClass() on it, there'd be no need to tell it?