How To Print A Character Random Number Of Times

I'm trying to write a method that will print a string of a random number of X's (from 5 to 20) on a line, then another number of X's on the next line, etc. until the random number = 16.

I have to use while loops and probably fencepost algorithms. I'm confused with how to print the number of x's the random number of times over and over.

Right now, I'm pretty sure my for loop is wrong or unnecessary.

So far, this is my code:

public static void randomX() {
int x = 0;
while (x != 16) {
x = (int)(Math.random()*20) + 5;
for (int i = 0; i <= x; i++);
{
System.out.print("x");
}
}
}