Java invert map

Question

I need create inverse map - select unique values and for them find keys. Seems that only way is to iterate all key/value pairs, because entrySet returns set of so value not

Answer 1

To get an inverted form of a given map in java 8:

public static  Map inverseMap(Map sourceMap) {
    return sourceMap.entrySet().stream().collect(
        Collectors.toMap(Entry::getValue, Entry::getKey,
           (a, b) -> a) //if sourceMap has duplicate values, keep only first
        );
}

Example usage

Map map = new HashMap();

map.put(1, "one");
map.put(2, "two");

Map inverted = inverseMap(map);