java空心菱形for循环

import java.util.Scanner;
public class klingxing{
public static void main(String[] args){
int x,y,z;
  int a,b,c;
  int m;
  System.out.println("请输入三角形的高:");
  Scanner sc = new Scanner(System.in);
  m = sc.nextInt();
  for(x=1;x<=m;x++){
   for(z=m+1;z>x;z--){
     System.out.print(" ");
   }
   for(y=1;y<=x;y++){
    if(x==y||y-1==0){
     System.out.print("* ");
    }
    else
     System.out.print("  ");
   }
   System.out.println();
  }
  for(a=m+1;a>0;a--){
   for(c=m+1;c>a;c--){
    System.out.print(" ");
   }
   for(b=1;b<=a;b++){
    if(a==b||b-1==0){
     System.out.print("* ");
    }
    else
     System.out.print("  ");
   }
   System.out.println();
  }
}
}