collection with Duplicate key

[Mohanasundar Nagarajan]

Hi,
Java reference says that a Map, HashMap or Hashtable does not allow to store multiple entries with a same key. I have the requirement to store multiple entries (basically key will repeat) into some collection with a same key. Is there any collection to handle such a situation?

Thanks in advance,
Mohanasundar.n

[John Jai]

If you need use the same key reference multiple values then think about making the values as a List.

So a sample might look like Map<String,List<Object>>.

[Jesper de Jong]

You could do what John Jai says, or use for example Multimap from Google Guava.

[Winston Gutkowski]

Jesper de Jong wrote:You could do what John Jai says, or use for example Multimap from Google Guava.

Yes, when is regular Java going to get a Multimap implementation?

@Mohana: Just to add a wrinkle to John's post, another option you might want to consider is a Map<Key,Set<Value>>. One slight advantage of that setup is that you can't store duplicate (ie, equal()) values for the same key, which may or may not be what you want. If it is, then it's probably the way to go.

Winston