Leetcode topic analysis spiral matrix II

Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.

For example,

Given n = 3,

You should return the following matrix:

[

1, 2, 3 ,

8, 9, 4 ,

7, 6, 5

]

    public int[][] generateMatrix(int n) {
        if (n <= 0) {
            return new int[0][0];
        }
        int[][] matrix = new int[n][n];
        int num = 1;
        int startx = 0, endx = n - 1;
        int starty = 0, endy = n - 1;
        while (startx <= endx && starty <= endy) {
            //  Upper row , From left to right 
            for (int y = starty; y <= endy; y++) {
                matrix[startx][y] = num++;
            }
            //  The column on the right , From top to bottom 
            for (int x = startx + 1; x <= endx; x++) {
                matrix[x][endy] = num++;
            }
            //  If rows or columns are traversed , Then exit the loop 
            if (startx == endx || starty == endy) {
                break;
            }
            //  Row below , From right to left 
            for (int y = endy - 1; y >= starty; y--) {
                matrix[endx][y] = num++;
            }
            //  The column on the left , From bottom to top 
            for (int x = endx - 1; x >= startx + 1; x--) {
                matrix[x][starty] = num++;
            }
            startx++;
            starty++;
            endx--;
            endy--;
        }
        return matrix;
    }