打印空心菱形

import java.util.Scanner;

public class KXLX {

public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.println("请输入一个数:");
int a = input.nextInt();

for (int i = 1; i <= a; i++) {
for (int k = 1; k <= a - i; k++) {
System.out.print(" ");
}
for (int j = 1; j <= 2 * i - 1; j++) {
if (j == 1 || j == 2 * i - 1) {
System.out.print("*");
} else {
System.out.print(" ");
}
}
System.out.println();
}

for (int i = a - 1; i >= 0; i--) {
for (int k = 1; k <= a - i; k++) {
System.out.print(" ");
}
for (int j = 1; j <= 2 * i - 1; j++) {
if (j == 1 || j == 2 * i - 1) {
System.out.print("*");
} else {
System.out.print(" ");
}
}
System.out.println();
}

}

}