Collections

Java使用Collections.reverse()反转一个List

public class Demo { 

public static void main(String[] args) { 
ArrayList<Integer> lists = new ArrayList<Integer>();
 // 初始化10个测试数据 
for (int i = 0; i < 10; i++) { 
lists.add(i); 
} 
// 打印测试数据
 for (Integer n : lists) {
 System.out.print(n + " ");
 } 
// 反转lists 
Collections.reverse(lists); 
// 换行打印 
System.out.println();
 // 打印测试数据 for (Integer n : lists) { 
System.out.print(n + " "); 
} 
} 
}

0 1 2 3 4 5 6 7 8 9 
9 8 7 6 5 4 3 2 1 0

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作者：张雨明
来源：CSDN
原文：https://blog.csdn.net/yu540135101/article/details/85258494
版权声明：本文为博主原创文章，转载请附上博文链接！

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import java.util.ArrayList;
import java.util.Collections;
 
 
public class TTEST {
    public static void main(String[] args) {
        ArrayList<String> arr = new ArrayList<String>();
        for(int i=0;i<10;++i){
            arr.add("str"+i);
        }
        for (String string : arr) {
            System.out.print(string+" ");
        }
        System.out.println();
        Collections.reverse(arr);
        for (String string : arr) {
            System.out.print(string+" ");
        }
    }
}

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作者：呼啸
来源：CSDN
原文：https://blog.csdn.net/howlaa/article/details/34809737
版权声明：本文为博主原创文章，转载请附上博文链接！

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Collections实现List集合排序

//将集合按照时间倒叙排序
Collections.sort(vo, new Comparator<OaDocmanage>() {


@Override
public int compare(OaDocmanage o1, OaDocmanage o2) {
return o2.getDate().compareTo(o1.getDate());
}

});


vo 是要排序的list集合；OaDocmanage是集合中存的对象； getDate是OaDocmanage的date属性的get方法


o1.getDate().compareTo(o2.getDate());    顺序排序


o2.getDate().compareTo(o1.getDate());    倒叙排序
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作者：鹏鹏博客
来源：CSDN
原文：https://blog.csdn.net/u013782879/article/details/80852818
版权声明：本文为博主原创文章，转载请附上博文链接！

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1：实现comparable

1. import java.util.ArrayList;
2. import java.util.Collections;
3. import java.util.List;
4.  
5. public class User implements Comparable<User> {
6.  
7. private int score;
8.  
9. private int age;
10.  
11. public User(int score, int age) {
12. super();
13. this.score = score;
14. this.age = age;
15. }
16.  
17. public int getScore() {
18. return score;
19. }
20.  
21. public void setScore(int score) {
22. this.score = score;
23. }
24.  
25. public int getAge() {
26. return age;
27. }
28.  
29. public void setAge(int age) {
30. this.age = age;
31. }
32.  
33. @Override
34. public int compareTo(User o) {
35. int i = this.getAge() - o.getAge();//先按照年龄排序
36. if (i == 0) {
37. return this.score - o.getScore();//如果年龄相等了再用分数进行排序
38. }
39. return i;
40. }
41.  
42. public static void main(String[] args) {
43. List<User> users = new ArrayList<User>();
44. users.add(new User(78, 26));
45. users.add(new User(67, 23));
46. users.add(new User(34, 56));
47. users.add(new User(55, 23));
48. Collections.sort(users);
49. for (User user : users) {
50. System.out.println(user.getScore() + "," + user.getAge());
51. }
52. }
53. }

  2 ：直接用匿名内部类

1. import java.util.ArrayList;
2. import java.util.Collections;
3. import java.util.Comparator;
4. import java.util.List;
5.  
6. public class Students {
7.  
8. private int age;
9. private int score;
10.  
11. public Students(int age, int score) {
12. super();
13. this.age = age;
14. this.score = score;
15. }
16.  
17. public int getAge() {
18. return age;
19. }
20.  
21. public void setAge(int age) {
22. this.age = age;
23. }
24.  
25. public int getScore() {
26. return score;
27. }
28.  
29. public void setScore(int score) {
30. this.score = score;
31. }
32.  
33. public static void main(String[] args) {
34. List<Students> students = new ArrayList<Students>();
35. students.add(new Students(23, 100));
36. students.add(new Students(27, 98));
37. students.add(new Students(29, 99));
38. students.add(new Students(29, 98));
39. students.add(new Students(22, 89));
40. Collections.sort(students, new Comparator<Students>() {
41.  
42. @Override
43. public int compare(Students o1, Students o2) {
44. int i = o1.getScore() - o2.getScore();
45. if (i == 0) {
46. return o1.getAge() - o2.getAge();
47. }
48. return i;
49. }
50. });
51. for (Students stu : students) {
52. System.out.println("score:" + stu.getScore() + ":age" + stu.getAge());
53. }
54. }
55. }