Getting an error with a game I created after reading chap 3.

[Naziru Gelajo]

Greetings everyone, with some of the material I learned (though I had to research how to do random number generation). I created a mini Craps game (it's a dice game). Unfortunately, even though the program compiles, it refuses to run. Here is the error I'm getting:

lamoubeldum@LamouBeldum:~/JavaPrograms/Projects$ java CrapsTest
Exception in thread "main" java.lang.NullPointerException
at CrapsTest.main(CrapsTest.java:12)
lamoubeldum@LamouBeldum:~/JavaPrograms/Projects$

Here is my code, everything compiles just fine:

//code for CrapsTest.java

public class CrapsTest {
   public static void main (String [] args) {
      int randomroll1;
      int randomroll2;
      int rolltotal;

      Dice [] d = new Dice [2]; //Create an array comprised of 2 dice


        d[0].roll(); //Initiate a roll for the first dice in the array
        d[0].rollnum = (int) ((Math.random() * 6) + 1);
        randomroll1 = d[0].rollnum;


        d[1].roll(); //Initiate a roll for the second dice in the array
        d[1].rollnum = (int) ((Math.random() * 6) + 1);
        randomroll2 = d[1].rollnum;

        rolltotal = randomroll1 + randomroll2; //Calculate the sum of both dice rolled in order to verify a win or loss    
            if ( rolltotal == 7 || rolltotal == 11) {
               System.out.println("You rolled a " + rolltotal);
               System.out.println("Congratulations, you have won the game!");
            }
            else {
               System.out.println("You rolled a " + rolltotal);
               System.out.println("Too bad, you didn't win! Try again!");
            }
      }
}


class Dice { //create a Dice object to be referenced to in other parts of the code

   int rollnum;

   void roll() {
        System.out.println("Get ready to roll some dice, If you roll a 7 or 11 you Win!");
   }

}

Is there anything I'm not seeing, maybe you Java Heroes can shed some light on the situation Thanks!

[Carey Brown]

Dice [] d = new Dice [2];

This creates an array of references but until you initialize them the references are null;
You'll need something like

d[0] = new Dice( ... );

[Naziru Gelajo]

Carey Brown wrote:

Dice [] d = new Dice [2];

This creates an array of references but until you initialize them the references are null;
You'll need something like

d[0] = new Dice( ... );

Excellent, thank you very much!