Java combining two hashmaps of the same type into a new hashmap keeping duplicates

Assume we are given:

Map<String, String> map1 = new HashMap<>();  map1.put("111","Frank");  map1.put("222","Ted");  map1.put("555","Peter");    Map<String, String> map2 = new HashMap<>();  map2.put("333","Roger");  map2.put("222","Ted");  map2.put("888","Kent");  map2.put("555","Peter");  

How could I go about combining both of these into a new map:

Map<String, String> combinedMap = new HashMap<>();  

I wanted to do it in a java stream way, so my attempt was:

combinedMap = Stream.of(map1, map2)                          .flatMap(m -> m.entrySet().stream())                          .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));  

But I was hit with some duplicate key error. I believe I could also just do a combinedMap.putAll(map1) and combinedMap.putAll(map2) but I'm not sure if that's the best way possible.

https://stackoverflow.com/questions/66862960/java-combining-two-hashmaps-of-the-same-type-into-a-new-hashmap-keeping-duplicat March 30, 2021 at 07:33AM