数组排序

1、问题描述：现有user实体，有名称name和age两个属性，先想实现对arrayList<User>数组按照年龄进行排序。

2、user实体代码如下，重写tostring方法方便排序后数组的输出。

package com.fengshu.test.action;

import org.junit.Test;

public class User implements Comparable<User>
{
    private String name;
    private int age;

    @Test
    public void fengshu()
    {
        double i = 4.0;
        String s = String.valueOf(i);
        System.out.print(s);

    }

    User(String _name, int _age)
    {
        name = _name;
        age = _age;

    }

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

    public String getName()
    {
        return name;
    }

    public int getAge()
    {
        return age;
    }

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

    @Override
    public int compareTo(User o)
    {
        return name.compareTo(o.getName());
    }
    public String toString()
    {
        return name;
    }
}

3、排序类如下

　　

package com.fengshu.test.action;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

import org.junit.Test;

public class SortUser implements Comparator<User>
{
    @Test
    public void sort()
    {
        SortUser sortUser = new SortUser();
        sortUser.sort();
    }
    public static void main(String[] args)
    {
        
        ArrayList<User> userList = new ArrayList<User>();
        User[] users = new User[5];
        users[0] = new User("fengshu", 4);
        users[1] = new User("feng", 9);
        users[2] = new User("lizhifeng", 5);
        users[3] = new User("jim", 33);
        for (int i = 0; i < 4; i++)
        {
            userList.add(i, users[i]);
        }
        //Collections.sort(userList);
        Collections.sort(userList, new SortUser());
        System.out.print(userList);
    }
    @Override
    public int compare(User o1, User o2)
    {
        return o1.getAge()-o2.getAge();
    }

}