JAVA秒会技术之Java8新特性利用流快速处理集合的常见操作

Posted 2022-12-04 Ethan_LiYan

例子1：对集合进行排序

List<Integer> list = Lists.newArrayList(1,1,2,2,5,3,4,6,6,5,2,7);
list.sort(null);
list.forEach(e -> System.out.print(e)); //输出结果：112223455667

例子2：对集合过滤

List<Integer> list = Lists.newArrayList(1,1,2,2,5,3,4,6,6,5,2,7);
list.removeIf(s-> s.equals(2));
list.forEach(e -> System.out.print(e)); //输出结果：115346657

例子3：集合1中的元素，同时存在在集合2中的（注意不会去重）

List<Integer> list1 = Lists.newArrayList(1,1,2,2,5,3,4,6,6,5,2,7);
List<Integer> list2 = Lists.newArrayList(1,1,3,5,7,8);
list1.retainAll(list2);
list1.forEach(e -> System.out.print(e)); //输出结果：115357

例子4：集合去重

List<Integer> list = Lists.newArrayList(1,1,2,2,5,3,4,6,6,5,2,7);
list = list1.stream().distinct().collect(Collectors.toList());
list.forEach(e -> System.out.print(e)); //输出结果：1253467

例子5：集合过滤（2）

List<Integer> list1 = Lists.newArrayList(1,1,2,2,5,3,4,6,6,5,2,7);
list1 = list1.stream().filter(s -> !s.equals(2)).collect(Collectors.toList());
list1.forEach(e -> System.out.print(e)); //输出结果：115346657

例子6：集合映射

User user1 = new User();
user1.setId(1);
user1.setUserName("张三");
User user2 = new User();
user2.setId(2);
user2.setUserName("李四");
User user3 = new User();
user3.setId(3);
user3.setUserName("王五");
User user4 = new User();
user4.setId(4);
user4.setUserName("赵六");
User user5 = new User();
user5.setId(5);
user5.setUserName("田七");
ArrayList<User> userList = Lists.newArrayList(user1,user2,user3,user4,user5);

List<String> userNameList = userList.stream().map(User :: getUserName).collect(Collectors.toList());
userNameList.forEach(e -> System.out.println(e)); //输出结果：张三 李四 王五 赵六 田七

例子7：List集合转换成Map集合

User user1 = new User();
user1.setId(1);
user1.setUserName("张三");
User user2 = new User();
user2.setId(2);
user2.setUserName("李四");
User user3 = new User();
user3.setId(3);
user3.setUserName("王五");
User user4 = new User();
user4.setId(4);
user4.setUserName("赵六");
User user5 = new User();
user5.setId(5);
user5.setUserName("田七");
ArrayList<User> userList = Lists.newArrayList(user1,user2,user3,user4,user5);

Map<Integer, String> userMap = userList.stream().collect(Collectors.toMap(User :: getId, User :: getUserName));
userMap.forEach((key,value) -> 
	System.out.println(key + ":" + value);
); //输出结果：1:张三 2:李四 3:王五 4:赵六 5:田七

其实流的应用还有很多，很强大，但是也有很多坑，大家自行摸索吧！