java.lang.ArrayIndexOutOfBoundsException？

Question

我目前正在通过一本教科书自学一些基本的 Java 并给自己一个 "homework problem" 但是我在写入方法的 .txt 文件时遇到了困难。它不想占用超过 2 个人。以下是该方法的用途的简要运行：

1.) 收集用户希望输入数据文件的人数

2.) 将每个人的名字和姓氏收集到一个二维数组中

3.) 收集用户为用户输入数组的每个（单独）人设置的付款数。

4.) 然后它计算输入另一个数组的每个人的平均付款（所以每个人应该有自己的平均值）

5.) 最后，它将数据写入名为 "BusinessData.txt."

的 .txt 文件

在尝试将超过 2 个人写入 .txt 文件之前，它似乎运行良好。这让我抓狂，我真的很想知道如何解决这个问题，然后再继续接下来的几个主题。

这是我在尝试添加超过 2 个人时收到的错误消息：

Exception in thread "main" java.lang.Array IndexOutofBoundsException: 3
at Business1.dataCollect(Business1.java:210)
at Business1.main(Business1.java:62)

如果有任何提示，我将不胜感激。

这是实际代码：

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

public class Business1
{
    public static void main(String[] args) throws IOException
    {
        // Declare local variables
        int menuChoice;

        // Declare local objects
        Scanner input = new Scanner(System.in);

        // Display the program title
        System.out.println("\n\n\n\n\t\t\t\t***************************************\n"
                                +  "\t\t\t\t* Average Customer Payment Calculator *\n"
                                +  "\t\t\t\t***************************************\n\n\n");

        // Start of a do-while loop: Continues the program as long as the user doesn't choose to exit
        do
        {
            // Start of a do-while loop: Input Validation (menuChoice must be between 1 - 4)
            do
            {

                // Prompt user for menuChoice
                System.out.print("\tPlease enter an integer in accordance to the given choices:\n\n"
                                 + "\t(1) Collect and Erase Old Data\n"
                                 + "\t(2) Read Saved Data\n"
                                 + "\t(3) Append Old Data\n"
                                 + "\t(4) Exit Program\n\n"
                                 +"\tEnter Choice: ");

                menuChoice = input.nextInt();
                System.out.println("\n\n");


                // If menuChoice is equal to 1: Erase old Data and Collect and Write new data
                if(menuChoice == 1)
                {
                    try
                    {
                        dataCollect();
                    }

                    catch(IOException e)
                    {
                        System.out.println("Error");
                    }
                }
                // else if menuChoice is equal to 2: Read Saved Data
                else if(menuChoice == 2)
                {

                } 
                // else if menuChoice is equal to 3: Append Old Data
                else if(menuChoice == 3)
                {

                }
                // else if menuChoice is equal to 4: Exit Program
                else if(menuChoice == 4)
                {
                    System.out.println("\n\n\n\t\tGoodbye!\n\n\n");
                }

                // else display error message: Error. Please enter a number 1 - 4 
                else
                {
                    System.out.println("\n\nERROR. Please enter a number 1 - 4\n\n");
                }

            // End of do-while loop: Input Validation (menuChoice must be between 1 - 4)
            } while(menuChoice < 1 || menuChoice > 4);
        // End of a do-while loop: Continues the program as long as the user doesn't choose to exit
        } while(menuChoice != 4);
    }

    // Create a method named dataCollect
    public static void dataCollect() throws IOException
    {
        // Declare local variables
        int numPeople, numPayments /* array size for payments */;
        double totalPayments = 0, averagePayment;
        double [] paymentsArray  /* different payments */, averagePaymentsArray;
        String [][] namesArray /* First name, last name in array */;

        // Declare objects
        Scanner keyboard = new Scanner(System.in);


        // Prompt user for the number of people they would like to add to the records and store in variable numPeople
        System.out.print("\tHow many people would you like to add to your records?\n\n\tEnter an integer: ");
        numPeople = keyboard.nextInt();
        System.out.println("\n\n");

        // Initialize arrays
        namesArray = new String[numPeople][2];


        // Create a counter for the for-loop
        int count = 0;
        // For-loop will prompt user for first and last name of each person
        for(int i = 1; i <= numPeople; i++)
        {

            // Consume the remaining newline character
            keyboard.nextLine();

            // Prompt user for first name
            System.out.print("\tPlease enter the FIRST name of person #" + i  +": ");
            namesArray[count][0] = keyboard.nextLine();
            System.out.println("\n\n");

            //Prompt user for last name
            System.out.print("\tPlease enter the LAST name of person #" + i + ": ");
            namesArray[count][1] = keyboard.nextLine();
            System.out.println("\n\n\n");

            count++;
        }

        // Reset counter for the next for-loop
        count = 0;
        int count2 = 1; // Used to keep track of which payment number the user is inputing
        int count3 = 0; 
        int count4 = -1;


        // ****************************************************************
        // * Open file for input ******************************************
        // ****************************************************************

        PrintWriter outputFile = new PrintWriter("BusinessData.txt");
        outputFile.println("\t\t\tBusiness Data\n\n");
        outputFile.println("First Name\tLast Name\tP 1\t\tP 2\t\t P 3\t\tAverage Payments\n\n"
                        +  "------------------------------------------------------------------------------------------------------------------------------------------------------\n");

        // For-loop will ask for number of payments each person made while also collecting the value of each of those payments in a nested for-loop.
        for(int i = 0; i < numPeople; i++)
        {
            // Prompt user for first name
            System.out.print("\tPlease enter the number of payments made by " + namesArray[count][0] +" " + namesArray[count][1] + "(Put in 3 for now) : ");
            numPayments = keyboard.nextInt();


            System.out.println("\n\n");

            // Initialize array then reset it for the next person to come
            paymentsArray = new double[numPayments];

                for(int j = 0; j < numPayments; j++)
                {
                    // ****************************************************************
                    // * Open file for input ******************************************
                    // ****************************************************************

                    System.out.print("\n\n\tPlease enter payment value of payment #" + count2 + " that " + namesArray[count][0] +" " + namesArray[count][1] + " made: $");
                    paymentsArray[j] = keyboard.nextDouble();
                    System.out.println("\n\n");

                    // Increment counter
                    count2++;
                }

                    // ************************************************************************
                    // * Calculating Average Payment ******************************************
                    // ************************************************************************

                    // For loop for calculating average
                    for(int k = 0; k < numPayments; k++)
                    {
                        totalPayments += paymentsArray[k];
                    }

                    // Calculate the Average Payment
                    averagePayment = totalPayments/paymentsArray.length;

                    /**************************************************
                     ********** BUG LIES IN THE WRITING  **************
                    ***************************************************/


                    // nested for-loop will write data now otherwise it'll just be wiped out and overwritten by the next input
                    for(int l = 1; l < numPeople; l++)
                    {   

                        // Increment counter4
                        count4++;
                        // Output first name
                        outputFile.print(namesArray[count4][count3]);

                        // Increment counter3
                        count3++;

                        // Output last name
                        outputFile.print("\t\t" + namesArray[count4][count3] + "\t\t");
                        // Reset counter3
                        count3 = 0;


                        for (int m = 0; m < numPayments; m++)
                        {
                            outputFile.print(paymentsArray[m] + "\t\t");
                        }

                        outputFile.println(averagePayment + "\n\n");
                    }


             // Reset total Payments for the next iteration
            totalPayments = 0.0;

            // Increment the counter
            count++; 
        }
        outputFile.close();

    // End of dataCollect method
    }

Answer 1

运行您的代码为我提供了 3 个以上用户的例外。在

抛出 ArrayIndexOutOfBoundsException

  outputFile.print(namesArray[count4][count3]);

运行在调试模式下显示 namesArray[count4][count3] 指向一个不可用的值。

由于下面的循环，count4 增加到越界值。

我不明白你为什么需要这个循环

for(int l = 1; l < numPeople; l++)
                { 
enter code here}

如果删除它，它会正常工作。

java.lang.ArrayIndexOutOfBoundsException？

java.lang.ArrayIndexOutOfBoundsException?

java

nested-loops

multidimensional-array

file-writing