The flatMap function is very similar to the map function, but it is used when the operation might return more than one value and we want to keep a stream of single elements. In the case of map, a stream of collections would be returned instead. Let's see flatMap in use:
@Testpublic void gettingLettersUsedInNames() { List<String> names = Arrays.asList("Alex", "Paul", "Viktor"); List<String> lettersUsed = Collections.emptyList(); assertThat(lettersUsed) .hasSize(12) .containsExactly("a","l","e","x","p","u","v","i","k","t","o","r");}
One possible solution could be:
List<String> lettersUsed = names.stream() .map(String::toLowerCase) .flatMap(name -> Stream.of(name.split(""))) .distinct() .collect(Collectors.toList());
This time we have ...
