Java8新特性介紹

過濾集合

 List<String> newList = list.stream().filter(item -> item != null).collect(Collectors.toList());

找出並返回集合中重複的元素

ArrayList<Integer> list = new ArrayList<>();
		list.add(1);
		list.add(1);
		list.add(2);
		list.add(3);
Set<Integer> collect = list.stream().filter(i -> list.stream().filter(i::equals).count() > 1).collect(Collectors.toSet());
 

返回物件陣列某一元素構成的集合

	List<String> list1 = list.stream().map(User::getUsername).collect(Collectors.toList());

根據某一元素去重

 ArrayList<EmdBageOrderListDto> distinctList = list.stream().collect(Collectors.collectingAndThen(
                                    Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(User::getUsername))), ArrayList::new));
 

根據集合某個屬性分組並存入map

  Map<String, List<User>> bageOrderMap = list.stream().collect(Collectors.groupingBy(User::getUsername));

型別轉換

List轉String

String str = list.stream().collect(Collectors.joining(","))

List<String>轉List<Integer>

//方法一
List<Integer> intList = strList.stream().map(Integer::parseInt).collect(Collectors.toList());

//方法二
 List<Integer> intStream = strList.stream().mapToInt(Integer::parseInt).boxed().collect(Collectors.toList());