How to map values in a map in Java 8? [duplicate]

Solution 1:

You need to stream the entries and collect them in a new map:

Map<String, String> result = map.entrySet()
    .stream()
    .collect(Collectors.toMap(Entry::getKey, e -> String.valueOf(e.getValue()));

Solution 2:

The easiest way to do so is:

Map<String, Integer> map = new HashMap<>();
Map<String, String> mapped = map.entrySet().stream()
        .collect(Collectors.toMap(Map.Entry::getKey, entry -> String.valueOf(entry.getValue())));

What you do here, is:

1. Obtain a Stream<Map.Entry<String, Integer>>
2. Collect the results in the resulting map:
   1. Map the entries to their key.
   2. Map the entries to the new values, incorporating String.valueOf.

The reason you cannot do it in a one-liner, is because the Map interface does not offer such, the closest you can get to that is map.replaceAll, but that method dictates that the type should remain the same.