How to Inverse a Map with Duplicate Keys/Values-CodePudding

I have a map with duplicate values and different keys. I want to reverse a map but want to retain the values associated to keys. It'll be more clear from below:

Original Map -

{key1=value1, key2=value1, key3=value2}

Expected Output -

{value1=key1, value1=Key2, value2=key3}

    Map<String, String> map = new HashMap<>();
    map.put("key1","value1");
    map.put("key2","value1");
    map.put("key3","value2");

    System.out.println(map);
    
    Map<String, String> inverseMap = MapUtils.invertMap(map); 
    System.out.println(inverseMap);

I am getting only {value1=key2, value2=key3} as duplicate keys are not allowed in maps. So is there any way get the expected output.

Thanks in Advance!

CodePudding user response：

you can't., keys cant be duplicates

1st you are assigning value1=key1

2n time when u assign value1= key2

"key1" is replaced by "key2"

CodePudding user response：

Picking up on @shmosel's idea of using Guava:

Multimap<String, String> inverseMap = ImmutableListMultimap.copyOf(map.entrySet()).inverse();
System.out.println(inverseMap);
System.out.println(inverseMap.entries());

This prints:

{value1=[key1, key2], value2=[key3]}
[value1=key1, value1=key2, value2=key3]

A Multimap is

A collection that maps keys to values, similar to Map, but in which each key may be associated with multiple values.