Need some explanation on 2D String arrays

Question

In the nested for loop for a basic 2D String array I came across this:

 array = new String [5][10];
for(int i=0; i<array.length;i++)
{
    for(int j=0; j<array[0].length;j++)
    {
        System.out.print(array[i][j]="*");
    }
    System.out.println("");
}

Now this is what I want to know, why does the second for statement include array[0].length rather than array.length like in the for statement before it?

All I could extract from this while experimenting was if both for statements contained array.length and the 2D array was a 5x10, it would print it as a 5x5, but with array[0].length it would print a correct 5x10.

So why does this little adjustment fix everything?

Answer 1

You're dealing with a 2D array. array.length essentially gives you the number of rows, but array[0].length gives the number of columns (at least for non-jagged arrays). Take this example:

String[][] array = new String[][]{
    {"1","2"},
    {"3","4"},
    {"5","6"}
};

Here array.length is 3 (the entire 2D-array is composed of three 1D-arrays), but array[0].length is 2 (the length of each constituent array). Your first for-loop loops over the whole array-of-arrays, but your second loops over each constituent array that is encountered by the outer loop. Therefore, the inner loop should only loop up to (but not including) array[0].length.