Java中List集合排序的方法 比较器的使用 根据学生对象数序 语文 英语成绩总和进行sort排序

Posted 2020-10-20 Advancing Swift

package com.swift;

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

public class Test2_ObjectIO {

    @SuppressWarnings("unchecked")
    public static void main(String[] args) {

        /*
         * 第2题: 有五个学生，每个学生有3门课（语文、数学、英语）的成绩，写一个程序接收从键盘输入学生的信息，
         * 输入格式为：name,30,30,30（姓名，三门课成绩），然后把输入的学生信息按总分从高到低的顺序写入到一个名称"stu.txt"文件中。
         * 要求：stu.txt文件的格式要比较直观，打开这个文件，就可以很清楚的看到学生的信息。
         */
        List<Student> list = new ArrayList<Student>();
        Scanner scan = new Scanner(System.in);
        for (int i = 1; i <=5; i++) {
            System.out.println("请输入第"+i+"学生信息：格式为 name 60 60 60");
            String name = scan.next();
            Float yuwen = scan.nextFloat();
            Float shuxue = scan.nextFloat();
            Float yingyu = scan.nextFloat();
            Student stu = new Student(name, yuwen, shuxue, yingyu);
            list.add(stu);
        }
        
        for(Student stu:list) {
            System.out.println(stu.toString());
        }
        
        Collections.sort(list, new Comparator<Student>() {

            @Override
            public int compare(Student o1, Student o2) {
                float num=(o2.getShuxue()+o2.getYingyu()+o2.getYuwen())-(o1.getShuxue()+o1.getYingyu()+o1.getYuwen());
                int i=(int) num;
                return i;
            }
        });
        
        for(Student stu:list) {
            System.out.println(stu.toString());
        }
    }
}

class Student {
    private String name;
    private float yuwen;
    private float shuxue;
    private float yingyu;

    public String getName() {
        return name;
    }

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

    public float getYuwen() {
        return yuwen;
    }

    public void setYuwen(float yuwen) {
        this.yuwen = yuwen;
    }

    public float getShuxue() {
        return shuxue;
    }

    public void setShuxue(float shuxue) {
        this.shuxue = shuxue;
    }

    public float getYingyu() {
        return yingyu;
    }

    public void setYingyu(float yingyu) {
        this.yingyu = yingyu;
    }

    public Student(String name, float yuwen, float shuxue, float yingyu) {
        super();
        this.name = name;
        this.yuwen = yuwen;
        this.shuxue = shuxue;
        this.yingyu = yingyu;
    }

    public Student() {
        super();
    }

    @Override
    public String toString() {
        return "Student [name=" + name + ", yuwen=" + yuwen + ", shuxue=" + shuxue + ", yingyu=" + yingyu + "]";
    }

}

比较器就是个匿名内部类，Collections.sort(list,Comparator<Student>(){});

然后实现其中的compare方法，返回一个int类型的值，正数 负数 0分别代表大于小于等于

增加IO流的内容代码如下；

package com.swift;

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.UnsupportedEncodingException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.Scanner;

public class Test2_ObjectIO {

    @SuppressWarnings("unchecked")
    public static void main(String[] args) {

        /*
         * 第2题: 有五个学生，每个学生有3门课（语文、数学、英语）的成绩，写一个程序接收从键盘输入学生的信息，
         * 输入格式为：name,30,30,30（姓名，三门课成绩），然后把输入的学生信息按总分从高到低的顺序写入到一个名称"stu.txt"文件中。
         * 要求：stu.txt文件的格式要比较直观，打开这个文件，就可以很清楚的看到学生的信息。
         */
        List<Student> list = initiateList();
        
        for(Student stu:list) {
            System.out.println(stu.toString());
        }
        
        Collections.sort(list, new Comparator<Student>() {

            @Override
            public int compare(Student o1, Student o2) {
                float num=(o2.getShuxue()+o2.getYingyu()+o2.getYuwen())-(o1.getShuxue()+o1.getYingyu()+o1.getYuwen());
                int i=(int) num;
                return i;
            }
        });
        
        initiate_IO(list);
        
        
    }

    private static void initiate_IO(List<Student> list) {
        BufferedWriter bw;
        StringBuffer sb=new StringBuffer();
        for(Student stu:list) {
            sb.append(stu.toString());
            sb.append("\r\n");
        }
        try {
            bw = new BufferedWriter(new OutputStreamWriter(new FileOutputStream("src\\stu.txt"),"utf-8"));//需要标明路径
            bw.write(sb.toString());
            bw.flush();
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } 
        
    }

    private static List<Student> initiateList() {
        List<Student> list = new ArrayList<Student>();
        Scanner scan = new Scanner(System.in);
        for (int i = 1; i <=5; i++) {
            System.out.println("请输入第"+i+"学生信息：格式为 name 60 60 60");
            String name = scan.next();
            Float yuwen = scan.nextFloat();
            Float shuxue = scan.nextFloat();
            Float yingyu = scan.nextFloat();
            Student stu = new Student(name, yuwen, shuxue, yingyu);
            list.add(stu);
        }
        return list;
    }
}

class Student {
    private String name;
    private float yuwen;
    private float shuxue;
    private float yingyu;

    public String getName() {
        return name;
    }

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

    public float getYuwen() {
        return yuwen;
    }

    public void setYuwen(float yuwen) {
        this.yuwen = yuwen;
    }

    public float getShuxue() {
        return shuxue;
    }

    public void setShuxue(float shuxue) {
        this.shuxue = shuxue;
    }

    public float getYingyu() {
        return yingyu;
    }

    public void setYingyu(float yingyu) {
        this.yingyu = yingyu;
    }

    public Student(String name, float yuwen, float shuxue, float yingyu) {
        super();
        this.name = name;
        this.yuwen = yuwen;
        this.shuxue = shuxue;
        this.yingyu = yingyu;
    }

    public Student() {
        super();
    }

    @Override
    public String toString() {
        return "Student [name=" + name + ", yuwen=" + yuwen + ", shuxue=" + shuxue + ", yingyu=" + yingyu + "]";
    }

}