Spiral Matrix II

public class Solution {    public int[][] generateMatrix(int n) {        if (n < 0) {            return null;        }        int[][] matrix = new int[n][n];        int row = 0;        int col = 0;        int num = 1;        while (n > 0) {            if (n == 1) {                matrix[row][col] = num++;            }            for (int i = 0; i < n - 1; i++) {                matrix[row][col + i] = num++;            }            for (int i = 0; i < n - 1; i++) {                matrix[row + i][col + n - 1] = num++;            }            for (int i = 0; i < n - 1; i++) {                matrix[row + n - 1][col + n - 1 - i] = num++;            }            for (int i = 0; i < n - 1; i++) {                matrix[row + n - 1 - i][col] = num++;            }            row++;            col++;            n -= 2;        }        return matrix;    }}