java - 如何将包含字符串和整数的文件读入 ArrayList 并按整数排序？

Question

我正在尝试从包含按行组织的姓名和成绩列表的文本文件中读取，即:

大卫·史密斯 84

苏珊 L 波特 100

...

然后将它们(按行)存储在 ArrayList 中，并使用选择排序算法按学生的成绩对 ArrayList 进行排序，但是我尝试了多种不同的编码方式，每次编辑似乎都会提示另一个错误(我对编程非常陌生)。这是我目前拥有的:

import java.io.*;
import java.util.*;

public class Grades {
    private static void sort(ArrayList<String> list) {
        int pFill;
        int pTest;
        int pSmallest;
        String temp;
        for (pFill = 0; pFill < list.size(); pFill++) {
            pSmallest = pFill;
            for (pTest = pFill + 1; pTest < list.size(); pTest++) {
                if (pTest < pSmallest) {
                    pSmallest = pTest;
                }
            }
            temp = list.get(pSmallest);
            list.set(pSmallest, list.get(pFill));
            list.set(pFill, temp);
        }
    } 

    public static void main(String[] args){
        ArrayList<String> list = new ArrayList<>();
        String fileName = "students.txt";
        try (BufferedReader input = new BufferedReader(new FileReader(fileName))) {
            while(input.ready()){
                list.add(input.readLine());
            }
            input.close();
            sort(list);
            System.out.println(list);
        } catch (IOException e){
                System.out.println(e.getMessage());
        }
    }
}

Answer 1

您可以创建一个学生对象来分别保存姓名和成绩。将所有数据添加到列表后，您可以通过使用 Comparator 直接使用 list.sort() 方法。但在您的情况下，您想编写选择排序，这就是为什么您必须编写另一种方法来进行选择排序的原因。

package com.stackovflow.problems;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;

public class Grades {

        public static void main(String[] args){
            ArrayList<Student> list = new ArrayList<>();
            String fileName = "students.txt";
            try (BufferedReader input = new BufferedReader(new FileReader(fileName))) {
                while(input.ready()){
                    String line = input.readLine().trim();
                    String name = line.substring(0,line.lastIndexOf(' '));
                    int grade = Integer.parseInt(line.substring(line.lastIndexOf(' ')+1));
                    list.add(new Student(name, grade));
                }
                input.close();
                selectionSort(list);
                System.out.println(list);
            } catch (IOException e){
                    System.out.println(e.getMessage());
            }
        }

        private static void selectionSort(ArrayList<Student> list) {
            int pFill;
            int pTest;
            int pSmallest;
            Student temp;
            for (pFill = 0; pFill < list.size(); pFill++) {
                pSmallest = pFill;
                for (pTest = pFill + 1; pTest < list.size(); pTest++) {
                    Student pTestStudent = list.get(pTest);
                    Student pSmallestStudent = list.get(pSmallest);
                    if (pTestStudent.getGrade() < pSmallestStudent.getGrade()) {
                        pSmallest = pTest;
                    }
                }
                if(pSmallest!=pFill) {
                    temp = list.get(pSmallest); 
                    list.set(pSmallest, list.get(pFill));
                    list.set(pFill, temp);
                }
            }

        }
    }

//This class is to hold line data in your students.txt file
class Student{
    private String name;
    private int grade;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getGrade() {
        return grade;
    }
    public void setGrade(int grade) {
        this.grade = grade;
    }
    public Student(String name, int grade) {
        super();
        this.name = name;
        this.grade = grade;
    }
    @Override
    public String toString() {
        return "Student [name=" + name + ", grade=" + grade + "]";
    }

}