what java collection that provides multiple values for the same key

Question

what type of java collection that returns multiple values for the same key?

example, I want to return 301,302,303 for key 300.

Answer 1

You could use Multimap, it is under the Apache license.

See this link. For posterity:

org.apache.commons.collections
Interface MultiMap

All Superinterfaces:
    java.util.Map

All Known Implementing Classes:
    MultiHashMap, MultiValueMap

public interface MultiMap
extends java.util.Map

Defines a map that holds a collection of values against each key.

A MultiMap is a Map with slightly different semantics. Putting a value into the map will add the value to a Collection at that key. Getting a value will return a Collection, holding all the values put to that key.

For example:

 MultiMap mhm = new MultiHashMap();
 mhm.put(key, "A");
 mhm.put(key, "B");
 mhm.put(key, "C");
 Collection coll = (Collection) mhm.get(key);

coll will be a collection containing "A", "B", "C".