Test-Driven Java Development, Second Edition - Second Edition

map

The map function transforms all the elements in the stream into another. The resultant object can share the type with the input, but it's also possible to return an object of a different type:

@Testpublic void mapToUppercaseTransformsAllElementsToUppercase() {  List<String> names = Arrays.asList("Alex", "Paul", "Viktor");  List<String> namesUppercase = Collections.emptyList();  assertThat(namesUppercase)      .hasSize(3)      .containsExactly("ALEX", "PAUL", "VIKTOR");}

The list namesUppercase should be computed as follows:

List<String> namesUppercase = names.stream()  .map(String::toUpperCase)  .collect(Collectors.toList());

Note how the toUpperCase method is called. It belongs to the Java class String and can be used in that scenario only by referencing ...