Multi-key storage

Question

are there any map or list, anything that can store data with same key?
Thanks.
Vincent

Answer 1

I usually just put a List into the Map against the given key:
public void add(Object key, Object item)
  List list = (List)map.get(key);
  if(list == null)
    list = new ArrayList();
    map.put(key, list);
  list.add(item);
public void remove(Object key, Object item)
  List list = (List)map.get(key);
  if(list != null)
    list.remove(item);
public Iterator get(Object key)
  List list = (List)map.get(key);
  if(list != null)
    return list.iterator();
  return null;
}I know it's not quite the Map interface but you'll always differ from the API slightly since your get method doesn't return what was put in. The remove method could maybe do with some alteration so that it doesn't require a key.
Hope this helps.