java - Iterating over List in a Map -

what best way iterate on "de-normalized" map of collections?

for example, have following map:

map<string, list<string>> relations; 

in order iterate on each key -> each value like:

for (entry<string,list<string>> e : relations.entries()) {    (string s : e.getvalue()) {        system.out.println(e.getkey() + " - " + s);    } } 

is there elegant way solve decorator or so?

i'm hoping find like:

for(entry e : collections.getdenormalizeentriesfrommapofcollection(mymap)) {    system.out.println(e.getkey() + " - " + e.getvalue()); } 

that give same result, on second situation have 1 entry each key -> collection item.

i recommend @ guavas multimap implementation. have kind of iterator:

to transform map<k, collection<v> multimap<k, v> can use utility method:

public static <k,v> multimap<k,v> tomultimap(map<k,? extends collection<v>> m) {      linkedlistmultimap<k, v> multimap = linkedlistmultimap.create();      (entry<k, ? extends collection<v>> e : m.entryset())         multimap.putall(e.getkey(), e.getvalue());      return multimap; } 

---

usage:

public static void main(string[] args) {      map<string, list<integer>> map = new hashmap<string, list<integer>>();      map.put("hello", arrays.aslist(1, 2));     map.put("world!", arrays.aslist(3));      multimap<string, integer> multimap = tomultimap(map);      iterator<entry<string, integer>> = multimap.entries().iterator();      while (it.hasnext())         system.out.println(it.next()); } 

outputs:

hello=1 hello=2 world=3