Question

当程序到达for循环并尝试运行时，我收到错误

for (int m = 0; m < students; m++){
        allScores = allScores + scores[m];

学生被宣布为int allScores被声明为双倍，得分[]数组。

这是错误消息：

线程“main”中的异常java.lang.ArrayIndexOutOfBoundsException：2 在Lab4.main（Lab4.java:51）

第51行是for（int m = 0; m＆lt; students; m ++）line

编辑：

这是我的整个代码，我可能没有正确完成score []数组：

import java.util.*;
import java.text.*;

public class Lab4 {
public static void main(String[] args){
    Scanner s= new Scanner(System.in);
    String input;
    int students;
    int d=1;
    double allScores = 0;

    char [] answerKey= { 'B' , 'D' , 'A' , 'A' , 'C' , 'A' , 'B' , 'A' , 'C' , 'D' , 'B' , 'A' };
    char [] userAnswers = new char[answerKey.length];

    DecimalFormat df = new DecimalFormat("#0.0");

    System.out.print("how many students are in the class? ");
    input = s.nextLine();
    students=Integer.parseInt(input);

    String [] name = new String[students];
    double [] scores = new double[students];

    for (int j = 0; j < students; ++j)
    {
        int correctAnswers=0;

        System.out.print("Enter name of student " + (j + 1) + ": ");
        name[j] = s.nextLine();

        System.out.print("Enter quiz score answers :");
        String line = s.nextLine().toUpperCase();
        for (int k = 0; k < answerKey.length; k++) {
        userAnswers[k] = line.charAt(k);
            }


            for (int i = 0; i < userAnswers.length; i++)
        {

                if(userAnswers[i] == answerKey[i])
                {
                    correctAnswers++;
                }



        }
            System.out.println(name[j]);
            System.out.println((df.format((((float)(correctAnswers) / answerKey.length)) * 100)) + "%");
            scores [d] = ((float)((correctAnswers) / answerKey.length) * 100);
            d++;
    }
    System.out.println("the high score is "   + "and the low score is "   );
    for (int m = 0; m < scores.length; m++){
        allScores = allScores + scores[m];
    }
    System.out.println("Average is:" + ((allScores/students)));

}

}

编辑：

对不起，我读错了第51行的行

scores [d] = ((float)((correctAnswers) / answerKey.length) * 100);

编辑：

新代码不再向我提供错误消息，但我似乎无法获得分数的平均值。

import java.util.*;
import java.text.*;

public class Lab4 {
public static void main(String[] args){
    Scanner s= new Scanner(System.in);
    String input;
    int students;
    int d=1;
    double allScores = 0;

    char [] answerKey= { 'B' , 'D' , 'A' , 'A' , 'C' , 'A' , 'B' , 'A' , 'C' , 'D' , 'B' , 'A' };
    char [] userAnswers = new char[answerKey.length];

    DecimalFormat df = new DecimalFormat("#0.0");

    System.out.print("how many students are in the class? ");
    input = s.nextLine();
    students=Integer.parseInt(input);

    String [] name = new String[students];
    double [] scores = new double[students + 1];

    for (int j = 0; j < students; ++j)
    {
        int correctAnswers=0;

        System.out.print("Enter name of student " + (j + 1) + ": ");
        name[j] = s.nextLine();

        System.out.print("Enter quiz score answers :");
        String line = s.nextLine().toUpperCase();
        for (int k = 0; k < answerKey.length; k++) {
        userAnswers[k] = line.charAt(k);
            }


            for (int i = 0; i < userAnswers.length; i++)
        {

                if(userAnswers[i] == answerKey[i])
                {
                    correctAnswers++;
                }



        }
            System.out.println(name[j]);
            System.out.println((df.format((((float)(correctAnswers) / answerKey.length)) * 100)) + "%");
            scores [d] = ((float)((correctAnswers) / answerKey.length) * 100);
            d++;
    }
    System.out.println("the high score is "   + "and the low score is "   );
    for (int m = 0; m < scores.length; m++){
        allScores = allScores + scores[m];
    }
    System.out.println("Average is:" + ((allScores/students)));

}

}

Answer 1

问题是students被初始化为大于scores.length的值。您可以使用scores.length代替students作为循环的上限;或者，将students初始化为scores.length（或低于它的东西）。

如果您只想迭代整个数组，可以使用enhanced for loop语法：

for (double score : scores) {
    allScores = allScores + score;
}

编辑我自己计算了一些线条（有点单调乏味），我就登上了这条线：

scores [d] = ((float)((correctAnswers) / answerKey.length) * 100);

发生的事情是d太大了。这可能是因为您将d初始化为1而不是0。

Answer 2

在数组中使用length属性进行迭代。

for (int m = 0; m < scores.length; m++){
        allScores = allScores + scores[m];

但是，您提到错误发生在第51行，但第51行是：

scores [d] = ((float)((correctAnswers) / answerKey.length) * 100);

所以你的d等于或大于scores.length。

我很好奇你为什么用1？

初始化d

将其更改为0可能会解决问题。

int d=0;

代码中的另一个问题是：

((float)((correctAnswers) / answerKey.length) * 100);

将其更改为

(((float)correctAnswers / answerKey.length) * 100);

否则，您更改结果，该结果已经是浮点数的int。这将影响结果。

Answer 3

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException:

这是因为您访问超出限制的数组。可能在scores[m];

您可以使用以下内容：

for (int m = 0; m < scores.length; m++){
        allScores = allScores + scores[m];

Answer 4

您的代码存在一些不符之处：

int d=1; // your score[index] starts with this just change to 0;

scores [d] = ((float)((correctAnswers) / answerKey.length) * 100);

//your scores length will now be d + students; use the students instead
for (int m = 0; m < scores.length; m++){  //for (int m=0;m<students;m++)
        allScores = allScores + scores[m];
    }

困惑的for循环

4 个答案: