merge - Merging two Map<String, Integer> with Java 8 Stream API -

i have 2 (or more) map<string, integer> objects. i'd merge them java 8 stream api in way values common keys should maximum of values.

@test public void test14() throws exception {     map<string, integer> m1 = immutablemap.of("a", 2, "b", 3);     map<string, integer> m2 = immutablemap.of("a", 3, "c", 4);     list<map<string, integer>> list = newarraylist(m1, m2);      map<string, integer> mx = list.stream()... // todo      map<string, integer> expected = immutablemap.of("a", 3, "b", 3, "c", 4);     assertequals(expected, mx); } 

how can make test method green?

i've played collect , collectors while without success.

(immutablemap , newarraylist google guava.)

@test public void test14() throws exception {     map<string, integer> m1 = immutablemap.of("a", 2, "b", 3);     map<string, integer> m2 = immutablemap.of("a", 3, "c", 4);      map<string, integer> mx = stream.of(m1, m2)         .map(map::entryset)          // converts each map entry set         .flatmap(collection::stream) // converts each set entry stream,                                      // "concatenates" in place of original set         .collect(             collectors.tomap(        // collects map                 map.entry::getkey,   // each entry based                 map.entry::getvalue, // on entries in stream                 integer::max         // such if value exist                                      // given key, max of old                                      // , new value taken             )         )     ;      /* use following if want create map parallel streams     map<string, integer> mx = stream.of(m1, m2)         .parallel()         .map(map::entryset)          // converts each map entry set         .flatmap(collection::stream) // converts each set entry stream,                                      // "concatenates" in place of original set         .collect(             collectors.toconcurrentmap(        // collects map                 map.entry::getkey,   // each entry based                 map.entry::getvalue, // on entries in stream                 integer::max         // such if value exist                                      // given key, max of old                                      // , new value taken             )         )     ;     */      map<string, integer> expected = immutablemap.of("a", 3, "b", 3, "c", 4);     assertequals(expected, mx); }