ArrayIndexOutOfBoundsException，同时将2D数组条目初始化为0

Question

I need to create a dynamic 2D array which the user can edit. I've tried many different ways and even tried to do it separately to easier diagnose, but always get a java.lang.ArrayIndexOutOfBoundsException . Below is some code (not from my project) that shows the problem. I get the error when I try to fill the board with 0 .

public class Example {
    public static void main (String args[]) {
        int rows = 0;
        int cols = 0;
        int[][] board = new int[rows][cols];
        Scanner scan = new Scanner (System.in);

        System.out.print("Enter in a row  :");
        rows = scan.nextInt();
        System.out.print("Enter in a col :");
        cols =scan.nextInt();

        for (int i = 0; i < rows; i++)  {
            for (int j = 0; j < cols; j++)  {
            board[i][j] = 0;
                    System.out.print ("\t" + board[i][j]);                       
                } 
            System.out.print ("\n"); 
            }
        }
    }

Answer 1

You're initializing the array with 0 rows and 0 columns. That's having place for nothing. If a user inputs 1 and 1 for rows and columns, you try to access the first row. But there is no row.

You should initialize your board after getting the amount of rows and columns from the user.

int rows = 0; // the Java default value for integers is 0. Equivalent: int rows;
int cols = 0; // equivalent: int cols;

Scanner scan = new Scanner (System.in);

System.out.print("Enter in a row  :");
rows = scan.nextInt();
System.out.print("Enter in a col :");
cols =scan.nextInt();

int[][] board = new int[rows][cols]; // now has values other than 0

for (int i = 0; i < rows; i++)
{
   for (int j = 0; j < cols; j++) 
   {
      board[i][j] = 0;
      System.out.print ("\t" + board[i][j]);                         
   } 
   System.out.print ("\n"); 
}

Ideally, you would want to verify user input to see that they give dimensions that make sense.

Answer 2

Of course you get an ArrayIndexOutOfBoundsException . You are initializing your array with [0][0] dimensions. Take a closer look at what values rows and cols have.

Allow a maximum of n rows and m cols.
eg int rows = 5, cols = 6

or just move your array initalization after you've read rows and cols from the Scanner .

int rows = Integer.MAX_VALUE;
int cols = Integer.MAX_VALUE;

Answer 3

If think, it should be something like this:

public class Example {

    public static void main (String args[]) { 
        int rows = 0; 
        int cols = 0; 
        Scanner scan = new Scanner (System.in);

       System.out.print("Enter in a row  :");
       rows = scan.nextInt();
       System.out.print("Enter in a col :");
       cols = scan.nextInt();

       int[][] board = new int[rows][cols]; 

       for (int i = 0; i < rows; i++)
       {
           for (int j = 0; j < cols; j++) 
           {
               board[i][j] = 0;
               System.out.print ("\t" + board[i][j]);                         
           } 
           System.out.print ("\n"); 
       }
    } 
}