Returning a HashMap K, M from a method of a class typed M

Question

So, this is what I have. I have a class parameterized for a bean type of a collection it receives, and in a method of the class, I need (would like) to return a HashMap typed as <K, M> as in:
public class MyClass<M> {
   private Collection<M> beanList;
   public HashMap<K, M> getMap(  /* what do I do here */ );
}I tried to cheat from looking at the Collections.sort method, knowing it uses the List type in its return type as in:
public static <T extends Comparable<? super T>> void sort(List<T> list)So, I am trying:
public HashMap<K, M> getMap(Class<K> keyType)But, it is telling me I need to create class K.
So... how does the Collections.sort method get away with it and I can't????
I suppose I could write the method as:
public HashMap<Object, M> getMap()but became somewhat challenged by my first guess.
Any ideas... or just go with the HashMap with the untyped key?

Answer 1

ejp wrote:
provided K is inferable from the arguments.Or from the assignment context:
Set<String> empty = Collections.emptySet();
Otherwise you have to parameterise the class on <K, M>.You may also specifically provide K when you use the method if the context doesn't give the compiler enough information or if you want to override it.
Example:
Set<Object> singleton1 = Collections.singleton("Hello"); //error
Set<Object> singleton2 = Collections.<Object>singleton("Hello"); //fineEdited by: endasil on 14-May-2010 4:13 PM