列印一個空心菱形

[code=Java]import java.io.InputStreamReader;


public class Work ...{
    public static void main(String[] args) throws IOException ...{
            int len; // 菱長
            String outstr=new String(); // 輸出
            int i,j,x,y; 
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            System.out.println("請輸入一個菱長:");
            String str = br.readLine();
            len=Integer.parseInt(str);             
            for(i=0;i<=len*2;i++)...{ 
            for(j=0;j<=len*2;j++)...{ 
            x=len-i; 
            x=x<0?-1*x:x; 
            y=len+(len-x); 
            outstr+=(j==x||j==y?"*":"　"); 
            } 
            outstr+=" "; 
            } 
            System.out.println(outstr); 
            } 
}
[/code]