Question

我有一个由15个学生对象组成的数组，其中包含一个int（学生ID）和一个数组（5个实验作业的分数）。我需要计算5个实验室中每个实验室的低，高和平均分数。我能想到的唯一方法是按列查看所有数组，但我的数组是每个学生的一行。我将如何在这些阵列上进行这些计算。包括Student对象数组来自的Util类和用于定义对象的Student类。我只需要提供的Statistics类的帮助。任何帮助将不胜感激！

Util.class：

import java.io.*;
import java.util.*;
import java.lang.*;
public class Util {
   public static Student[] readFile(String fileName) {
         Student studentArray[]=new Student[15];
         try{
            FileReader file = new FileReader("studentData.txt");
            BufferedReader buff = new BufferedReader(file);
            String line;
            line = buff.readLine();
            int index=0;
            while(line != null){
               System.out.println(line);
               if(index>14){
                  break;
               }
               line = buff.readLine();
               String[] result = line.split("\\s");
               int sid = Integer.parseInt(result[0]);
               int scores[] = new int[5];
               for(int x=1;x<result.length;x++){
                  scores[x-1] = Integer.parseInt(result[x]);
               }
               Student myCSC20Student = new Student(sid, scores);
               studentArray[index++] = myCSC20Student;
            }
         }
         catch (IOException e){
            System.out.println("Error: " + e.toString());
         } 
         return studentArray;  
      }    
   }

Student.class：

import java.io.*;
import java.util.*;
public class Student {
   final int LABS = 5;
   private int SID;
   private int scores[] = new int[LABS];   


   public Student(int sid, int[] scores)
    {
      this.SID=sid;
      this.scores = scores;
    }

   //getters and setters for SID and scores
   public int getID() {
      return SID;
   }
   public void setID(int x) {
      this.SID = x;
   }
   public int[] getScore() {
      return scores;
   }  
}

Statistics.class：

import java.io.*;
import java.util.*;
public class Statistics {
   final int LABS = 5;
   public int[] lowscores = new int[LABS];
   private int[] highscores = new int[LABS];
   private float[] avgscores = new float[LABS];
   public static void main(String args[]) {
   Student[] studArr = Util.readFile("studentData.txt");

   System.out.println("");

   for(int i=0; i<=studArr.length-1; i++){
      System.out.println(Arrays.toString(studArr[i].getScore()));
   }

   }

   void calculateLow(Student[] a){

   }
   void calculateHigh(Student[] a){

   }
   void calculateAvg(Student[] a){

   }
}

输出类：

import java.util.*;
public class Output{
   public static void main(String[] args){
      Student[] studArr = Util.readFile("studentData.txt");
      Statistics statistics = new Statistics();
      statistics.calculateLow(studArr);
      statistics.calculateHigh(studArr);
      statistics.calculateAvg(studArr);
      System.out.println("Low scores:");
      System.out.println(Arrays.toString(statistics.getLowscores()));
      System.out.println("High scores:");
      System.out.println(Arrays.toString(statistics.getHighscores()));
      System.out.println("Average scores:");
      System.out.println(Arrays.toString(statistics.getAvgscores()));
   }

}

Output of scores of all 15 students for the 5 labs

Answer 1

import java.util.*;
public class Statistics {
    final int LABS = 5;
    public int[] lowscores = new int[LABS];
    private int[] highscores = new int[LABS];
    private float[] avgscores = new float[LABS];
    public static void main(String args[]) {
        Student[] studArr = Util.readFile("studentData.txt");
        System.out.println();
        for(int i=0; i<=studArr.length-1; i++){
            System.out.println(Arrays.toString(studArr[i].getScore()));
        }
        Statistics statistics = new Statistics();
        statistics.calculateLow(studArr);
        statistics.calculateHigh(studArr);
        statistics.calculateAvg(studArr);
        System.out.println("Low scores:");
        System.out.println(Arrays.toString(statistics.getLowscores()));
        System.out.println("High scores:");
        System.out.println(Arrays.toString(statistics.getHighscores()));
        System.out.println("Average scores:");
        System.out.println(Arrays.toString(statistics.getAvgscores()));

    }

    public void calculateLow(Student[] a){
        for (int i = 0; i < LABS; i++) {
            final int lab = i;
            lowscores[lab] = Arrays.stream(a)
                    .mapToInt(student -> student.getScore()[lab])
                    .min()
                    .orElse(0);
        }
    }
    public void calculateHigh(Student[] a){
        for (int i = 0; i < LABS; i++) {
            final int lab = i;
            highscores[lab] = Arrays.stream(a)
                    .mapToInt(student -> student.getScore()[lab])
                    .max()
                    .orElse(0);
        }
    }
    public void calculateAvg(Student[] a){
        for (int i = 0; i < LABS; i++) {
            final int lab = i;
            avgscores[lab] = (float) Arrays.stream(a)
                    .mapToInt(student -> student.getScore()[lab])
                    .average()
                    .orElse(0);
        }
    }

    public int[] getLowscores() {
        return lowscores;
    }

    public int[] getHighscores() {
        return highscores;
    }

    public float[] getAvgscores() {
        return avgscores;
    }
}

Answer 2

@ Bogdan-Lukiyanchuk提供了一个利用Java流的解决方案。我的印象是，赋值仅用于循环和数组。因此，指向解决方案的指针类似于：

void calculateLow(Student[] a) {
  // if we don't have any students, then just leave
  if (a == null || a.length == 0) {
    return;
  }

  // set to the maximum score one could possibly have
  int lowScore = Integer.MAX_INT;
  Student lowPersonOnTotem = null;

  // process all of the students
  for (Student student : a) {
    int[] scores = student.getScore();

    // loop over all of the scores; if the score is lower than any 
    // previous, update the lowScore and who had it
    for (int score : scores) {
      if (score < lowScore) {
        lowScore = score;
        lowPersonOnTotem = student;
      }
    }
  }

   System.out.printf("Lowest score of all students is %d achieved by %d\n",
      lowScore, lowPersonOnTotem.getId());
}

现在，根据@markspace对评论的批评，我认为让calculateLow()返回一个值然后将显示放在其他地方是最合适的，但该方法被标记为void在OP的例子中。

其他方法基本上是相同的循环，但数学会改变。

需要在Object数组中对数组执行计算

2 个答案: