用字符串输入值填充二维数组

Question

I'm trying to fill a 2D array of String values with my own user inputs with Scanner .

Scanner s = new Scanner(System.in);
String[][] example = new String[20][10];

for (int x = 0; x < example.length; x++) {
    System.out.println("Enter name " + (x + 1) + ": ");
    example[x] = s.next();
}

I have no issues with filling in [][these ones] , but I'm having issues with the [these ones] . I need help with why this doesn't work and what I can do instead to fix it. I'm not super fluent so please try to keep things on the simpler side.

Answer 1

Don't forget you are allowed to use for-loops inside of for-loops. You can use this to your advantage to fill 2D-arrays. For example by using this code:

Scanner s = new Scanner(System.in);
String[][] example = new String[3][3];

for (int i = 0; i < example.length; i++) {
   for (int j = 0; j < example[0].length; j++) {
        example[i][j] = s.nextLine();
    }
}

Answer 2

When you're filling an array using loops you need two (nested) loops - one for the rows and one for the columns (typically in this order).

eg:

for (int row=0; row < twoDArray.length; row++) {
    for (int col=0; col < twoDArray[row].length; col++) {
        System.out.print("Enter name [" + (row+1) + "][" + (col+1) + "]: ");
        twoDArray[row][col] = s.next();
    }
}

Row/col are analogous to xy coordinates when drawing a chart.

To extend this further you could do the same for 3D, (and 4D, ... [N]D) arrays by adding a 3rd nested array... the looping would begin to get confusing but its exactly the same principal.

Answer 3

Okay, remember that String[][] is an array of an array of strings. That is, type type of example[0] is String[]. So you have to do a few things. This is the code I wrote:

public class Example {
    static int X = 5;
    static int Y = 2;

    public static void main(String[] args) {
        String[][] example = new String[X][Y];

        for (int outerIndex = 0; outerIndex < X; ++outerIndex) {
            // THIS LINE IS CRITICAL.
            example[outerIndex] = new String[Y];
            for (int innerIndex = 0; innerIndex < Y; ++innerIndex) {
                example[outerIndex][innerIndex] =
                    new String("("
                        + Integer.toString(outerIndex)
                        + ","
                        + Integer.toString(innerIndex)
                        + ")"
                    );
            }
        }

        for (int outerIndex = 0; outerIndex < X; ++outerIndex) {
            for (int innerIndex = 0; innerIndex < Y; ++innerIndex) {
                System.out.printf("%s    ", example[outerIndex][innerIndex]);
            }
            System.out.printf("\n");
        }
    }
}

Output:

$ javac Example.java && java Example
(0,0)    (0,1)
(1,0)    (1,1)
(2,0)    (2,1)
(3,0)    (3,1)
(4,0)    (4,1)

I didn't want to spew 200 values, so I used a smaller array size.