java8排序

一：对整数进行排序
List<Integer> numbers =Arrays.asList(6,2,1,4,9);
System.out.println(numbers);//[6, 2, 1, 4, 9]
numbers.sort(Comparator.naturalOrder());
System.out.println(numbers);//[1, 2, 4, 6, 9]
二、按字符串字段对列表进行排序
1. List<Movie> movies =Arrays.asList(
2. newMovie("Lord of the rings"),
3. newMovie("Back to the future"),
4. newMovie("Carlito's way"),
5. newMovie("Pulp fiction"));
6. movies.sort(Comparator.comparing(Movie::getTitle));
7. movies.forEach(System.out::println);
8. 提取的类型是String,而String实现了 Comparable接口,所以list能正确排序。
9. 三、按double字段排序列表
10. List<Movie> movies =Arrays.asList(
11. newMovie("Lord of the rings",8.8),
12. newMovie("Back to the future",8.5),
13. newMovie("Carlito's way",7.9),
14. newMovie("Pulp fiction",8.9));
15. movies.sort(Comparator.comparingDouble(Movie::getRating)
16. .reversed());
17. movies.forEach(System.out::println);
18. 我们使用反转函数( reversed)来反转默认从低到高的自然排序， Comparator.comparingDouble() 底层使用 Double.compare()实现。如果需要比较 int或 long，可以分别使用 comparisonInt()和 comparisonLong()。
19. 四、使用自定义比较器多列表进行排序
20. 1. List<Movie> movies =Arrays.asList(
  2. newMovie("Lord of the rings",8.8,true),
  3. newMovie("Back to the future",8.5,false),
  4. newMovie("Carlito's way",7.9,true),
  5. newMovie("Pulp fiction",8.9,false));
  6. movies.sort(newComparator<Movie>(){
  7. @Override
  8. publicint compare(Movie m1,Movie m2){
  9. if(m1.getStarred()== m2.getStarred()){
  10. return0;
  11. }
  12. return m1.getStarred()?-1:1;
  13. }
  14. });
  15. 我们可以使用 lambda表达式而不是匿名类( Anonymousclass)，如下所示:
  16. movies.forEach(System.out::println);
  17. 1. movies.sort((m1, m2)->{
    2. if(m1.getStarred()== m2.getStarred()){
    3. return0;
    4. }
    5. return m1.getStarred()?-1:1;
    6. });
    7. 也可以使用 Comparator.comparing():
    8. 1. movies.sort(Comparator.comparing(Movie::getStarred,(star1, star2)->{
      2. if(star1 == star2){
      3. return0;
      4. }
      5. return star1 ?-1:1;
      6. }));

List<Integer> numbers =Arrays.asList(6,2,1,4,9);
System.out.println(numbers);//[6, 2, 1, 4, 9]
numbers.sort(Comparator.naturalOrder());
System.out.println(numbers);//[1, 2, 4, 6, 9]

原文链接：https://dzone.com/articles/java-8-comparator-how-to-sort-a-list

作者： Mario Pio Gioiosa

译者：Steephan