JAVA中的回形针问题，其中最后一行代码不知道具体意义，求解答！

```public static void main(String[] args) {
        int n = 7;
        int[][] arr = new int[n][n];
        int count = 0;
        int maxX = n - 1;
        int maxY = n - 1;
        int minX = 0; 
        int minY = 0; 
        while (minX <= maxX) {
            for (int x = minX; x <= maxX; x++) {
                arr[minY][x] = ++count;
            }
            minY++;
            for (int y = minY; y <= maxY; y++) {
                arr[y][maxX] = ++count;
            }
            maxX--;
            for (int x = maxX; x >= minX; x--) {
                arr[maxY][x] = ++count;
            }
            maxY--;
            for (int y = maxY; y >= minY; y--) {
                arr[y][minX] = ++count;
            }
            minX++;
        }
        for (int i = 0; i < arr.length; i++) {
            for (int j = 0; j < arr.length; j++) {
                 String space = (arr[i][j] + "").length() == 1 ? "0" : "";  //这个位置的代码看不明白具体原因是什么。。。。
                System.out.print(space + arr[i][j] + " ");
            }
            System.out.println();
        }
    }
}