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 can use a List as the value of your Map:

List list = new ArrayList();
list.add(301);
list.add(302);
list.add(303);

Map> map = new HashMap>();
map.put(300, list);

map.get(300); // [301,302,303]

Alternatively, you can use Multimap from Guava, as suggested by biziclop, which has a much cleaner syntax, and lots of other very useful utility methods:

Multimap map = HashMultimap.create();
map.put(300, 301);
map.put(300, 302);
map.put(300, 303);

Collection list = map.get(300); // [301, 302, 303]