JAVA 使用Comparator接口实现自定义排序

1、原则

Comparator接口可以实现自定义排序，实现Comparator接口时，要重写compare方法：
int compare(Object o1, Object o2) 返回一个基本类型的整型
如果要按照升序排序,则o1 小于o2，返回-1（负数），相等返回0，01大于02返回1（正数）
如果要按照降序排序,则o1 小于o2，返回1（正数），相等返回0，01大于02返回-1（负数）

 import java.util.ArrayList;
 import java.util.Comparator;
 import java.util.List;

 public class UserComparator implements Comparator < User > {

     public static void main( String[] args ) {
         List < User > users = new ArrayList < User >();
         users.add( new User( 10, "a" ) );
         users.add( new User( 11, "d" ) );
         users.add( new User( 15, "s" ) );
         users.add( new User( 6, "x" ) );
         users.add( new User( 17, "a" ) );
         users.add( new User( 17, "b" ) );
         users.add( new User( 17, "c" ) );
         users.add( new User( 17, "d" ) );
         UserComparator comparator = new UserComparator();

         users.sort( comparator );
         // 也可以使用：Collections.sort( users, comparator );

         for ( User u : users ) {
             System.out.println( u );
         }
     }

     @Override
     public int compare( User u1, User u2 ) {
         if ( u1.equals( u2 ) ) {
             return 0;
         }
         else if ( u1.getAge() < u2.getAge() ) {
             return 1;
         }
         else if ( u1.getAge() == u2.getAge() ) {
             int f = u1.getName().compareTo( u2.getName() );
             if ( f < 0 ) {
                 return -1;
             }
             return 0;
         }
         else {
             return -1;
         }
     }
 }

 class User {
     private int age;
     private String name;

     public User() {

     }

     public User( int age, String name ) {
         this.age = age;
         this.name = name;
     }

     public int getAge() {
         return age;
     }

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

     public String getName() {
         return name;
     }

     public void setName( String name ) {
         this.name = name;
     }

     @Override
     public String toString() {
         return "User [age=" + age + ", name=" + name + "]";
     }

 }

User [age=17, name=a]
User [age=17, name=b]
User [age=17, name=c]
User [age=17, name=d]
User [age=15, name=s]
User [age=11, name=d]
User [age=10, name=a]
User [age=6, name=x]