comparable的compareTo( )方法 日常

Posted 2020-11-07 爬行的蜗牛

项目过程中遇到 类的排序 可以用这个类实现Comparable接口 ,重写comparaeTo方法来对这个类进行排序

在这个方法中 如果返回-1,则当前对象排在前面,如果返回1 ,则当前对象排在后面 ,返回0 .则相等

多的不说 直接上代码

实体类 :Student

import java.text.SimpleDateFormat;
import java.util.Date;

/**
 * @authot Administrator
 * @create 2018-05-20 13:43
 */
public class Student  implements Comparable<Student>{
    private Integer number;
    private Double money;
    private Date createdate;

    public  Student (Integer number,Double money,Date createdate) {
        this.number = number;
        this.money = money;
        this.createdate = createdate;
    }

    public Integer getNumber() {
        return number;
    }

    public Student setNumber(Integer number) {
        this.number = number;
        return this;
    }

    public Double getMoney() {
        return money;
    }

    public Student setMoney(Double money) {
        this.money = money;
        return this;
    }

    public Date getCreatedate() {
        return createdate;
    }

    public Student setCreatedate(Date createdate) {
        this.createdate = createdate;
        return this;
    }

    @Override
    public String toString() {
        return  "number:"+number+";money:"+money+";createdate:"+new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(createdate);
    }


    @Override
    public int compareTo(Student o) {
        if (this.number > o.number) {
            return -1;
        }else if (this.number < o.number) {
            return 1;
        }else{
            if (this.money > o.money) {
                return 1;
            }else if (this.money < o.money) {
                return -1;
            }else {
              return  this.createdate.compareTo(o.createdate);
            }
        }

    }
}

 里面三个字段 ,数量,总额,和创建时间 先比较数量 再比较总额 ,最后比较时间,一般到时间维度也就比较出来了

在比较时间的维度 的时候直接使用compareTo方法 因为在日期类中已经对compareTo方法做了重写 所以可以直接比较

测试类:

import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Date;
import java.util.List;

public class Main {

    public static void main(String[] args) throws Exception{
        List<Student> students = new ArrayList<Student>();
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        students.add(new Student(1,400.0,format.parse("2018-05-20 13:01:02")));
        students.add(new Student(2,300.0,format.parse("2018-05-20 13:20:02")));
        students.add(new Student(3,200.0,format.parse("2018-05-20 13:14:02")));
        students.add(new Student(4,100.0,format.parse("2018-05-20 13:16:02")));
        students.add(new Student(5,500.0,format.parse("2018-05-20 13:08:02")));
        students.add(new Student(5,500.0,format.parse("2018-05-20 13:08:03")));
        students.add(new Student(3,500.0,format.parse("2018-05-20 13:08:02")));
        students.add(new Student(1,600.0,format.parse("2018-05-20 13:08:02")));

        Collections.sort(students);

        for (Student student : students) {
            System.out.println(student);
        }
    }
}

运行结果如下:

number:5;money:500.0;createdate:2018-05-20 13:08:02
number:5;money:500.0;createdate:2018-05-20 13:08:03
number:4;money:100.0;createdate:2018-05-20 13:16:02
number:3;money:200.0;createdate:2018-05-20 13:14:02
number:3;money:500.0;createdate:2018-05-20 13:08:02
number:2;money:300.0;createdate:2018-05-20 13:20:02
number:1;money:400.0;createdate:2018-05-20 13:01:02
number:1;money:600.0;createdate:2018-05-20 13:08:02

 

第一次写博客希望可以对你得到帮助,多多指教