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]