如何在java中打印二维数组？

Question

I am stuck with this. I want to print an array with its size declared inside the code.

package userdefinedarray;

import java.util.Arrays;


public class userdefinedarray 
{    
    public static void main(String[] args) 
    {        
    int[][] myArray = new int[5][10];    
    for(int i=0;i<myArray.length;i++)
    {
        myArray[i] = null;
    }
    System.out.println(Arrays.toString(myArray));
    System.out.println(Arrays.deepToString(myArray));
}

}

Here's the output. What happened to the >>[10]<< in "new int[5][10]"?

[null, null, null, null, null]
[null, null, null, null, null]

Answer 1

Your 2-D array consists of arrays of arrays. Think of it in this way. For every array element imagine a new array as an element. So, in order to print it, you would need to iterate over each of those arrays, in other words, over rows and columns.

for(int i=0; i<myArray.length;i++){
    for(int j=0;j<myArray[0].length;j++)
       System.out.print(myArray[i][j] + " ");
    System.out.println();
}

If you want to fill your arrays with any particular non null value, you can do it inside the outer for loop.

Also, you cannot do

myArray[i] = null;

If you want to actually do that, use

myArray[i] = new int[myArray[0].length];

Answer 2

You are first creating an array containing 5 arrays having each 10 int (initialized to 0).

Then in your for loop, you set each index of the first dimension to null. You then have an array containing five null éléments.

If for some reason you really want to work with null values i advice you to use List instead.

If you want to set values of your array you should nest another loop inside the first one, but then setting to null the native int type will throw an exception i believe