5.15.4. Another Example: Dice

This sample class is by Ronnie Smith, with very minor revisions. The idea is that an object of class Dice can simulate rolling a single die. It relies on a pseudo-random number generator, which produces a sequence of apparently random numbers that are not really random at all.

import java.util.*;

public class Dice
{
   //===================================================
   // numSides is the number of sides that this die has.
   //
   // numRolls keeps track of the number of times this
   // die has been rolled.
   //
   // generator is a pseudo-random number generator.
   //===================================================

   private int numSides;
   private int numRolls=0;
   private Random generator = new Random();

   //===================================================
   // Constructors
   //===================================================

   //--------------------------------------------------
   // new Dice() returns a new 6-sided die.
   //--------------------------------------------------
   
   public Dice()
   {
     numSides = 6;
   }

   //--------------------------------------------------
   // new Dice(n) returns a new die with n sides.
   //--------------------------------------------------

   public Dice(int n)
   {
     numSides = n;
   }

   //===================================================
   // Accessors
   //===================================================

   //--------------------------------------------------
   // x.getNumSides() returns the number of sides of
   // die x.
   //--------------------------------------------------

   public int getNumSides() 
   {
     return numSides; 
   }

   //--------------------------------------------------
   // x.getNumRolls() returns the number of rolls 
   // stored in die x.
   //--------------------------------------------------

   public int getNumRolls() 
   {
     return numRolls; 
   }

   //===================================================
   // Mutators
   //===================================================
  
   //--------------------------------------------------
   // x.setNumSides(n) sets the number of sides of x
   // to n.
   //--------------------------------------------------

   public void setNumSides(int n) 
   {
     numSides = n;
   }

   //--------------------------------------------------
   // x.resetNumRolls sets the number of rolls in x
   // to 0.
   //--------------------------------------------------

   public void resetNumRolls()
   {
     numRolls = 0;
   }

   //===================================================
   // Actions
   //===================================================

   //--------------------------------------------------
   // x.roll() returns a pseudo-random number between
   // 1 and x.getNumSides(), inclusive.
   //--------------------------------------------------

   public int roll()
   {
     ++numRolls;
     return 1 + generator.nextInt(numSides);
   }
}

Using the Dice class

---

The following class illustrates how the Dice class can be used.

import java.util.*;

// Display rolls of 3 different dice, 1 set of rolls per line.
// The command line contains the number of sides of two of
// the dice.  The third has the default 6 sides.

public class DiceTest6
{
    public static void main(String[] args)
    {
       
        Dice die1 = new Dice(Integer.parseInt(args[0]));
        Dice die2 = new Dice(Integer.parseInt(args[1])); 
        Dice die3 = new Dice();

        Scanner keyboard = new Scanner(System.in);
        System.out.print("Enter number of rolls ");
        int timesToRoll = keyboard.nextInt();
        System.out.printf("%14s\n","Results");

        for (int rollNum = 1; rollNum <= timesToRoll; rollNum++)
        {
          System.out.printf("%5d %5d %5d\n",
                            die1.roll(),die2.roll(),die3.roll());
        }
    }
}