Reversing a HashMap from Map to Map>

Question

Is there a more elegant/built-in way to reverse the keys and values of a Hashmap?

I currently have the following.

private Map

        

Answer 1

I'd do something similar (but if you must do this kind of thing frequently, consider Guava), only replacing the List with Set (seems a little more consistent) and prefilling the reversemap:

private Map> reverseMap(Map permissions) {
    Map> returnvalue = new HashMap>();
    returnvalue.put(Boolean.TRUE, new HashSet());
    returnvalue.put(Boolean.FALSE, new HashSet());
    for (Entry entry : permissions.entrySet()) 
        returnvalue.get(entry.getValue()).add(entry.getKey());
    return returnvalue;
}