java打印菱形

自己写的自己都看不懂。。。

public class Demo2 {
    public static void main(String[] args) {

        // 打印菱形

        int rows = 6;

        int up = rows / 2 + 1;

        int down = rows / 2 - 1;


        for (int i = 1; i < up; i++) {
            for (int j = up - 1; j > i; j--) {
                System.out.print(" ");
            }

            for (int k = 0; k < i * 2 - 1; k++) {
                System.out.print("*");
            }

            System.out.println();
        }


        for (int i = 1; i <= down; i++) {
            for (int j = 0; j < i; j++) {
                System.out.print(" ");
            }

            for (int k = down * 2; k > i * 2 - 1; k--) {
                System.out.print("*");
            }

            System.out.println();

        }

    }
}