Question

我试图弄清楚为什么createArithmeticSeq中的循环越界，但无法弄明白。当i = listSize-1时，循环应该停止，因为它是（i = 0; i＆lt; listSize; i ++）。任何人都可以为我阐明这一点吗？

import java.util.*;

public class MagicSquare 
{
static int row, col, n, rows, columns, listSize;
static Scanner console = new Scanner (System.in);

这就是问题所在：

public static void createArithmeticSeq(int [] list)
    {   
    //prompt user for array size
    System.out.println("Enter size of array (in form nxn), n:");
    n = console.nextInt();
    rows = n;
    columns = n;
    listSize= (n*n);
    int first; 
    int diff;
    //prompt user for first and diff
    System.out.println("Enter first and diff : ");
    first = console.nextInt();
    diff  = console.nextInt();
    //process to create list of n*n elements 
    for (int i=0; i<listSize; i++)
    {
        list[i]=first+i*diff;
    }
}

以下是代码的其余部分：

public static void matricize (int [] list, int [][] matrix)
{
    int i = 0;
//loop through each row
    for (row=0; row<matrix.length; row++)
    {
    //loop through each column
        for (col=0; col<matrix[row].length; col++)
        {
        //populate matrix with values from list
        matrix[row][col] = list[i++];
        }
     }
}
public static void printMatrix(int [][] matrix)
{

    for (row=0; row < matrix.length; row++)
    {
        for (col=0; col < matrix[row].length; col++)
            System.out.printf("%2d" + " ", matrix[row][col]);

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

public static void reverseDiagonal(int [] [] matrix)
{ 
    int temp;
    for (row=0; row<matrix.length / 2; row++)
    {
        temp = matrix[row][row];
        matrix[row][row] = 
            matrix[matrix.length - 1 - row] [matrix.length - 1 - row];
        matrix[matrix.length - 1 - row][matrix.length - 1 - row] = temp;
    }
    for (row=0; row<matrix.length / 2; row++)
    {
        temp = matrix[row][matrix.length - 1 - row];
        matrix[row][matrix.length - 1 - row] = 
            matrix[matrix.length - 1 - row][row];
        matrix[matrix.length - 1 - row][row] = temp;
    }
}

public static void magicCheck(int [] list, int [] [] matrix)
{
    int sum=0, sumRow=0, sumCol=0, sumDiag1=0, sumDiag2=0, magicNumber=0;

    for(int i=0; i<listSize; i++)
    {
        sum += list[i]; 
        magicNumber = sum /= 4;

    for(row=0; row<matrix.length; row++)
    {
            //sum each row, then compare to magicNumber
        for(col=0; col<matrix[row].length; col++)
        sumRow = sumRow + matrix[row][col];
        while (sumRow == magicNumber)
        {
            for(col=0; col<matrix.length; col++)
            {
                for(row=0; row<matrix[col].length; row++)
                {
                sumCol = sumCol + matrix[row][col];
                    while (sumCol == magicNumber)
                    {
                    sumDiag1 = matrix[0][0]+matrix[1][1]+matrix[2][2]+matrix[3][3];
                        while (sumDiag1 == magicNumber)
                        {
                        sumDiag2 = matrix[3][0]+matrix[2][1]+matrix[1][2]
                        +matrix[0][3];
                            while(sumDiag2 == magicNumber)
                            System.out.println("It is a magic square.");
                        }
                    }
                }
            }
        }
    }
    }
            System.out.println("It is not a magic square.");

}

public static void main (String [] args)
{
    int [] list = new int [listSize];
    createArithmeticSeq (list);
    int [] [] matrix = new int [rows] [columns];
    matricize(list, matrix);
    printMatrix(matrix);
    System.out.print("\n");
    reverseDiagonal(matrix);
    printMatrix(matrix);
    magicCheck(list, matrix);   
}

}

Answer 1

在main中创建列表数组时，您正在使用listSize。由于您没有对其进行初始化，因此其值为0.

在createArithmeticSeq方法中，您将其大小更改为n*n，但这并不会影响仍为0的数组大小。

Answer 2

将listsize定义为static时，会获得默认值0。然后你调用createArithmeticSeq(int [] list)，你基本上传递一个包含0个元素空间的列表。如果在创建listsize后更改int [] list = new int [listSize];的值，则列表的大小不会更改。因此，您必须在知道它的大小后创建数组。

为此，请将主方法修改为

public static void main (String [] args)
{
    System.out.println("Enter size of array (in form nxn), n:");
    n = console.nextInt();
    rows = n;
    columns = n;
    listSize= (n*n);    
    int [] list = new int [listSize];
    createArithmeticSeq (list);
    int [] [] matrix = new int [rows] [columns];
    matricize(list, matrix);
    printMatrix(matrix);
    System.out.print("\n");
    reverseDiagonal(matrix);
    printMatrix(matrix);
    magicCheck(list, matrix);   
}

您的createArithmeticSeq方法为

public static void createArithmeticSeq(int [] list)
{   
    int first; 
    int diff;
    //prompt user for first and diff
    System.out.println("Enter first and diff : ");
    first = console.nextInt();
    diff  = console.nextInt();
    //process to create list of n*n elements 
    for (int i=0; i<listSize; i++)
    {
        list[i]=first+i*diff;
    }
}

Answer 3

在主体中，使用未初始化的“ listSize ”值创建列表数组，该值为0。因此，您应该更改代码，首先读取列表大小，然后创建数组：

public static void main (String [] args)
{
    //prompt user for array size
    System.out.println("Enter size of array (in form nxn), n:");
    n = console.nextInt();
    rows = n;
    columns = n;
    listSize= (n*n);

    int [] list = new int [listSize];
    createArithmeticSeq (list);
    int [] [] matrix = new int [rows] [columns];
    matricize(list, matrix);
    printMatrix(matrix);
    System.out.print("\n");
    reverseDiagonal(matrix);
    printMatrix(matrix);
    magicCheck(list, matrix);   
}

你的功能变为：

public static void createArithmeticSeq(int [] list)
{   
    int first; 
    int diff;
    //prompt user for first and diff
    System.out.println("Enter first and diff : ");
    first = console.nextInt();
    diff  = console.nextInt();
    //process to create list of n*n elements 
    for (int i=0; i<listSize; i++)
    {
        list[i]=first+i*diff;
    }
}

为什么这会生成Index Out of Bounds错误？

3 个答案: