I want to output all names starting with the letter "A" and sort them in reverse alphabetical order using the Stream API. The result should look like this: Ann, Andrew, Alex, Adisson. How do I do this?
List<List<String>> list = Arrays.asList( Arrays.asList("John", "Ann"), Arrays.asList("Alex", "Andrew", "Mark"), Arrays.asList("Neil", "Adisson", "Bob") ); List<List<String>> sortedList = list.stream() .filter(o -> o.startsWith("A")) Comparator.reverseOrder()); System.out.println(list); Since you are assigning the result to a List<List<String>> it appears you want to filter and sort each list and then print them. Here is how it might be done.
List<List<String>> sortedLists = list.stream() .map(lst -> lst.stream() .filter(o -> o.startsWith("A")) .sorted(Comparator.reverseOrder()).toList()) .toList(); for(List<String> lst : sortedLists) { System.out.println(lst); } prints (given your data).
[Ann] [Andrew, Alex] [Adisson] If, on the other hand you want to combine the lists into one applying the same requirements, then:
List<String> sortedList = list.stream().flatMap(List::stream) .filter(o->o.startsWith("A")) .sorted(Comparator.reverseOrder()) .toList(); for (String name : sortedList) { System.out.println(name); } prints
Ann Andrew Alex Adisson
List<String> sortedList = list.stream().flatMap(List::stream).filter(s -> s.startsWith("A")).sorted(Comparator.reverseOrder()).collect(Collectors.toList());