I'm trying to print this below pattern using nested loops in Java, but I'm having trouble getting it into the way it's supposed to look.

Code:
 *************
  ***********
   *********
    *******
     *****
      ***
       *
       *
      *** 
     *****
    *******     
   *********       
  ***********
 *************
There basically are two triangles, one going down and one going up. The first triangle starts out with 13 asterisks and then decrease by 2 each line until it gets to 1 asterisk. The second triangle begins with 1 asterisk and then increase until it reaches 13 asterisks.

This is the code that I have now.

Code:
class hourglass
{
	public static void main (String[] arguments)
	{
		//hourglass shape
		
        int size=13;
        int starStartPosition = 0;
        int starEndPosition = 13;
        String printout;
        for( int rows=0; rows<size; rows++)
        {
            for( int cols=0; cols<size; cols++)
            {
                if(cols < starStartPosition || cols >= starEndPosition)
                {
                    printout += " "; 
                }
                else
                {
                    printout += "*";
                }
            }
            if(rows <6)
            {
                starStartPosition++;
                starEndPosition--;
            }
            else
            {
                starStartPosition--;
                starPosition++;
            }
            System.out.println(printout);
            printout = "";
        }
    }
}
The above code only prints the single asterisk in the middle ONCE, but it should be printed TWICE since the shape is made up of TWO triangles. I am thinking of doing two separate nested loops for each individual triangle, but I have no idea how to do that or fix my current code.

Someone please help!
Thanks.