Java 8 - Stream

filter.java

  // filter(), findAny() and orElse()
Item item = items.stream()
    .filter(item -> Objects.equals(item.getId(), itemId))
    .findAny()
    .orElse(null);

// findFirst
Optional<Item> itemOpt = items.stream()
    .filter(item -> Objects.equals(item.getId(), itemId))
    .findFirst();
if(itemOpt.isPresent())
    Item item = itemOpt.get();

// filter() and collect()
List<Item> items = items.stream()
    .filter(item -> Objects.equals(item.getId(), itemId))
    .collect(Collectors.toList()); 

// filter() and map()
String name = persons.stream()
                .filter(x -> "jack".equals(x.getName()))
                .map(Person::getName)                        //convert stream to String
                .findAny()
                .orElse("");
 List<String> collect = persons.stream()
                .map(Person::getName)
                .collect(Collectors.toList());

// Array to Stream
//Arrays.stream
String[] array = {"a", "b", "c", "d", "e"};
Stream<String> stream1 = Arrays.stream(array);
stream1.forEach(x -> System.out.println(x));

//Stream.of
Stream<String> stream2 = Stream.of(array);
stream2.forEach(x -> System.out.println(x));

// Primitive Arrays
// 1. Arrays.stream -> IntStream
int[] intArray = {1, 2, 3, 4, 5};
IntStream intStream1 = Arrays.stream(intArray);
intStream1.forEach(x -> System.out.println(x));

// 2. Stream.of -> Stream<int[]>
Stream<int[]> temp = Stream.of(intArray);

// Cant print Stream<int[]> directly, convert / flat it to IntStream
IntStream intStream2 = temp.flatMapToInt(x -> Arrays.stream(x));
intStream2.forEach(x -> System.out.println(x));

// allMatch(), anyMatch(), noneMatch()

map.java

List<Long> ids = interviewSchedulings.stream().map(InterviewScheduling::getId).collect(Collectors.toList());
Long[] ids = interviewSchedulings.stream().map(InterviewScheduling::getId).toArray(Long[]::new)