If you wanted to keep that one die rolling 20 times, you would do the following:

/**  oneDieByTwenty - generates one throw of one die
*    uses a random number generator to do that
*  and it rolls 20 times
**/
public class oneDieByTwenty
{
      public static void main (String [] args)
      {
             double x; //  holds the random number we will generate
             int diceValue; // holds the value of the dice that we calculate from the random number
              int count;

              for (count = 0; count <20; count++)
              {
                  x = Math.random(); // generates a number between 0 and 1
                  x = x *6; //  multiplies that number times 6  so the number will be from 0 to 5
                  diceValue = (int) x; // convert it to integer to chop off the decimal portion
                  diceValue = diceValue +1; // with dice, we want 1-6, not 0-5, so we add 1
                  System.out.println ("The value of this die is " + diceValue);
               }
       }
}