Why the following piece of java code throws run time error?

Question

int[][] input = new int[3][];
int count = 1;

for(int i = 0; i <= 2 ; i++ ) {
    for(int j = 0; j <= 2; j++) {
        input[i][j] = count++;
    }
}

Fifth line throws an error.

Answer 1

Second dimension of the array is empty.

int[][] input = new int[3][];

Try this:

int[][] input = new int[3][3]; 

Answer 2

You need to initialize the second dimension

1) int[][] input = new int[3][3];

or

2)

for(int i = 0; i <= 2 ; i++ ){
    input[i] = new int[3];
}

Answer 3

Because you second array dimension is not specified.

This should run:

    int[][] input = new int[3][3];
    int count = 1;
    for(int i = 0; i <= 2 ; i++ ){
        for(int j = 0; j <= 2; j++){
            input[i][j] = count++;
        }
    }

See executable example

Answer 4

Because you didn't specify the second dimension size.

Answer 5

int[][] input = new int[3][];

this type of array are called ragged array. in you have to define the size of column for each row. like this:

input[0]=new int[2];//for row 1 (row 1 contain 2 column)
input[1]=new int[5];//for row 2 (row 2 contain 5 column)
input[2]=new int[1];// for row 3 (row 3 contain 1 column)

so define column size for each row as you wish

/*Ragged Arrays are multidimensional arrays in which the rows have different no of cols. */

 class Ragged
    {
     public static void main(String args[])
     {
       //declaration of a ragged array
       int arr[][] = new int[3][];
       //declaration of cols per row
       arr[0] = new int[4];
       arr[1] = new int[2];
       arr[2] = new int[3];

       int i, j;

       for(i =0; i< arr.length; i++)
       {
        for(j =0 ; j< arr[i].length; j++)
        {
           arr[i][j] = i + j+ 10;
        }
       }

       for(i =0; i< arr.length; i++)
       {
        System.out.println();//skip a line
        for(j =0 ; j< arr[i].length; j++)
        {
           System.out.print(arr[i][j]  + "  ");
        }
       }




//-------------more----------------
   int temp[];//int array reference
   //swap row2 and row3 of arr
   temp = arr[1];
   arr[1] = arr[2];
   arr[2] = temp;


   System.out.println();//skip a line
   for(i =0; i< arr.length; i++)
   {
    System.out.println();//skip a line
    for(j =0 ; j< arr[i].length; j++)
    {
       System.out.print(arr[i][j]  + "  ");
    }
   }

 }//main
}//class

/* TO declare a ragged array define a multi dimensional array with the val of last dimension missing.

The explicitly define the size of the last dimension for all the rows. */

Answer 6

You need specify size for second array during initialization. Also you can use .length property of array to avoid hard coded sizes.

int[][] input = new int[3][3];
int count = 1;

for(int i = 0; i <= input.length ; i++) {
    for(int j = 0; j <= input[i].length; j++) {
        input[i][j] = count++;
    }
}