public class ListStudy {
    public static void main(String[] args) {

        /**
         * --------------排序------------------
         */
        //------------简单数据类型排序--------------
        ArrayList<String> list = new ArrayList<>();
        list.add("12");
        list.add("8");
        list.add("9");
        list.add("20");
        list.add("4");
        Collections.sort(list); //降序：reverse()
        System.out.println("简单数据类型排序");
        System.out.println(list);
        /**
         *  字符串排序的规则：先从字符串中的第一个字符开始比较其编码的大小，
         *  按照升序排序。如果第一个相同比较第二个，如果第二个相同比较第三个.......
         */

        ArrayList<User> users = new ArrayList<>();
        users.add(new User("Tom", "20", 180));
        users.add(new User("Jack", "25", 170));
        users.add(new User("Jhon", "30", 160));
        users.add(new User("Lucy", "18", 165));
        users.add(new User("Made", "40", 172));

        //按照身高排序,升序：o1.getHeight()-o2.getHeight()，降序：o2.getHeight()-o1.getHeight()
        users.sort(new Comparator<User>() {
            public int compare(User o1, User o2) {
                return o1.getHeight() - o2.getHeight();
            }
        });
        //或直接使用lambda表达式：
        // users.sort(((o1, o2) -> o1.getHeight()-o2.getHeight()));
        // 方法引入：按身高顺序
        // users.sort(Comparator.comparingInt(User::getHeight));
        System.out.println("按照身高顺序：");
        Iterator<User> iterator = users.iterator();
        //快捷键：itit
        while (iterator.hasNext()) {
            User next = iterator.next();
            System.out.println(next);
        }

        //-------------按照年龄顺序排序，age是String--------------
        users.sort((u1, u2) -> u1.getAge().compareTo(u2.getAge()));
        //或 users.sort(Comparator.comparing(User::getAge));
        //或 users.sort(Comparator.comparing(User::getAge,(u1,u2)->u1.compareTo(u2)));
        System.out.println("按照年龄顺序：");
        Iterator<User> iterator1 = users.iterator();
        while (iterator1.hasNext()) {
            User next = iterator1.next();
            System.out.println(next);
        }

        //-------------按照年龄降序排序，age是String，用compareTo比较--------------
        users.sort((u1, u2) -> u2.getAge().compareTo(u1.getAge()));
        //或 users.sort(Comparator.comparing(User::getAge,((u1,u2)->u2.compareTo(u1))));
        //或 users.sort(Comparator.comparing(User::getAge,(Comparator.reverseOrder())));
        System.out.println("按照年龄倒序：");
        Iterator<User> iterator2 = users.iterator();
        while (iterator2.hasNext()) {
            User next = iterator2.next();
            System.out.println(next);
        }

    }
}


@Data
@NoArgsConstructor
@AllArgsConstructor
class User {
    private String name;
    private String age;
    private Integer height;
}
结果：
    
    
简单数据类型排序
[12, 20, 4, 8, 9]
按照身高顺序：
User(name=Jhon, age=30, height=160)
User(name=Lucy, age=18, height=165)
User(name=Jack, age=25, height=170)
User(name=Made, age=40, height=172)
User(name=Tom, age=20, height=180)
按照年龄顺序：
User(name=Lucy, age=18, height=165)
User(name=Tom, age=20, height=180)
User(name=Jack, age=25, height=170)
User(name=Jhon, age=30, height=160)
User(name=Made, age=40, height=172)
按照年龄倒叙：
User(name=Made, age=40, height=172)
User(name=Jhon, age=30, height=160)
User(name=Jack, age=25, height=170)
User(name=Tom, age=20, height=180)
User(name=Lucy, age=18, height=165)

Process finished with exit code 0

初始化集合的方法

/**
       * 初始化集合的方法：
       */
      List<String> list1=Arrays.asList(new String[]{"1","2","3"});

      List<String> list2= Arrays.asList("一","二","三");
      //JDK 8
      List<String> list3 = Stream.of("one", "two", "three").collect(Collectors.toList());
      //JDK 9
      List<Integer> list4 = lists.of(1, 2, 3);
      //匿名内部类
      List<Integer> list5 = new ArrayList<Integer>() {
          {
              add(1);
              add(2);
              add(3);
          }
      };
      //使用Google Guava工具集Lists(需要引入Guava工具包)
      List<Integer> list6 = Lists.newArrayList(1, 2, 3);