Using streams, how can I map the values in a HashMap?

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With Java 8 you can do:

Map<String, String> byNameMap = new HashMap<>();
people.forEach((k, v) -> byNameMap.put(k, v.getName());

Though you’d be better off using Guava’s Maps.transformValues, which wraps the original Map and does the conversion when you do the get, meaning you only pay the conversion cost when you actually consume the value.

Using Guava would look like this:

Map<String, String> byNameMap = Maps.transformValues(people, Person::getName);

EDIT:

Following @Eelco’s comment (and for completeness), the conversion to a map is better done with Collectors.toMap like this:

Map<String, String> byNameMap = people.entrySet()
  .stream()
  .collect(Collectors.toMap(Map.Entry::getKey, (entry) -> entry.getValue().getName());

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