list集合排序

https:/blog.csdn.net/veryisjava/article/details/51675036

 public static void main(String[] args) {
     List<Integer> nums = new ArrayList<Integer>();
         nums.add(3);
         nums.add(5);
         nums.add(1);
         nums.add(0);
         System.out.println(nums);
         Collections.sort(nums);
         System.out.println(nums);
 }  

test1

输出结果：
[3, 5, 1, 0]
[0, 1, 3, 5]

 package core.java.collection.collections;  

 public class User implements Comparable<User>{  

     private int score;  

     private int age;  

     public User(int score, int age){
         super();
         this.score = score;
         this.age = age;
     }  

     public int getScore() {
         return score;
     }  

     public void setScore(int score) {
         this.score = score;
     }  

     public int getAge() {
         return age;
     }  

     public void setAge(int age) {
         this.age = age;
     }  

     @Override
     public int compareTo(User o) {
         int i = this.getAge() - o.getAge();//先按照年龄排序
         if(i == 0){
             return this.score - o.getScore();//如果年龄相等了再用分数进行排序
         }
         return i;
     }  

 }  

 public static void main(String[] args) {
         List<User> users = new ArrayList<User>();
         users.add(new User(78, 26));
         users.add(new User(67, 23));
         users.add(new User(34, 56));
         users.add(new User(55, 23));
         Collections.sort(users);
         for(User user : users){
             System.out.println(user.getScore() + "," + user.getAge());
         }
 }  

test2

输出结果：
55,23
67,23
78,26
34,56

=======================

Collections提供的第二种排序方法sort(List<T> list, Comparator<? super T> c)

 package core.java.collection.collections;  

 public class Students {  

     private int age;
     private int score;  

     public Students(int age, int score){
         super();
         this.age = age;
         this.score = score;
     }  

     public int getAge() {
         return age;
     }
     public void setAge(int age) {
         this.age = age;
     }
     public int getScore() {
         return score;
     }
     public void setScore(int score) {
         this.score = score;
     }
 }
 public static void main(String[] args) {
         List<Students> students = new ArrayList<Students>();
         students.add(new Students(23, 100));
         students.add(new Students(27, 98));
         students.add(new Students(29, 99));
         students.add(new Students(29, 98));
         students.add(new Students(22, 89));
         Collections.sort(students, new Comparator<Students>() {  

             @Override
             public int compare(Students o1, Students o2) {
                 int i = o1.getScore() - o2.getScore();
                 if(i == 0){
                     return o1.getAge() - o2.getAge();
                 }
                 return i;
             }
         });
         for(Students stu : students){
             System.out.println("score:" + stu.getScore() + ":age" + stu.getAge());
         }
 }  

test3

输出结果：
score:89:age22
score:98:age27
score:98:age29
score:99:age29
score:100:age23

从上面的例子我们可以看出Students类没有实现Comparable<T>接口，只是在sort()方法
中多传入一个参数，只不过该参数是一个接口我们需要实现其compare方法。