Thread: Snake Eyes / Craps Dice games (JAVA)

Hello,
I am fairly new to java, roughly about three to four months in. I am having a problem with my java program. My goal is to request the user to enter how many times they want to roll a pair of dices. Each dice have numbers 1-6. When rolling the dices, I randomly pick a number from each dice and total the number. My goal is to calculate the number of times snake-eyes was rolled which is a total of 2 and total number of times a total of 7 was rolled. Here is my code. I am calling the rollDice method to perform the random pick and calculations. The error I am getting is at the bottom of the code. Any suggestions? Your help will be greatly appreciated.


package dice;
import java.util.Scanner;
import java.util.Random;

public class Dice
{
public static void main(String[] args)
{
int numRolls; // number of rolls

Scanner nord = new Scanner(System.in); // create InputStream
System.out.print("How many times would you like to roll the two dice? "); // prompt to enter how many times to roll dice
numRolls = nord.nextInt(); // variable to store number of rolls

// call rollDice method
rollDice(numRolls);
} //end main

public static void rollDice(int numRolls)
{
int d = numRolls;
int[] diceOne = null; // dice one variable
int[] diceTwo = null; // dice two variable
int crapsRolled = 0; // variable to hold how many times 7 was rolled
int snakeEysRolled = 0; // variable to hold how many times snake eyes was rolled
int totalDiceAmt; // count dice total
int[] diceRolls; // variable to store total number of dice rolls
int[] numArr = {1, 2, 3, 4, 5, 6}; // array to hold numbers on dice

// create an object from the Random class
Random r = new Random();

diceRolls = new int[d]; //create array to hold number of rolls

// loop through number of times you rolled
for (int i = 0; i < diceRolls.length; i++)
{
diceOne[i] = r.nextInt(numArr.length);
diceTwo[i] = r.nextInt(numArr.length);

totalDiceAmt = diceOne[i] + diceTwo[i];

// loop through number of times 2 was rolled
if (totalDiceAmt == 2)
{
snakeEysRolled++;
}
// loop through number of times 7 was rolled
if (totalDiceAmt == 7 )
{
crapsRolled++;
}
}

// print statement
System.out.println("Sneke Eyes was rolled " + snakeEysRolled + " times");
// print blank line
System.out.println();
System.out.println("Craps was rolled " + crapsRolled + " times");
} // end roll dice method
} // end Dice class


run:
How many times would you like to roll the two dice? 1000
Exception in thread "main" java.lang.NullPointerException
at dice.Dice.main(Dice.java:40)
Java Result: 1
BUILD SUCCESSFUL (total time: 4 seconds)

Thread moved.

Welcome to the Forum! Please read this topic to learn how to post code correctly and other useful tips for newcomers.

Please post your code correctly per the above link.

Sorry about that and thanks for providing this information on showing how to correctly post code in the forum. Here is the code I hope I’m posting it correctly this time.

package dice;
import java.util.Scanner;
import java.util.Random;
 
public class Dice 
{
    public static void main(String[] args) 
    {
        int numRolls;  // number of rolls
 
        Scanner nord = new Scanner(System.in); // create InputStream
        System.out.print("How many times would you like to roll the two dice? "); // prompt to enter how many times to roll dice        
        numRolls = nord.nextInt(); // variable to store number of rolls
 
        // call rollDice method
        rollDice(numRolls);
    } //end main
 
    public static void rollDice(int numRolls) 
    {   
        int d = numRolls; 
        int[] diceOne = null; // dice one variable
        int[] diceTwo = null; // dice two variable
        int crapsRolled = 0; // variable to hold how many times 7 was rolled
        int snakeEysRolled = 0;  // variable to hold how many times snake eyes was rolled
        int totalDiceAmt; // count dice total
        int[] diceRolls; // variable to store total number of dice rolls
        int[] numArr = {1, 2, 3, 4, 5, 6};  // array to hold numbers on dice
 
        // create an object from the Random class
        Random r = new Random();
 
        diceRolls =  new int[d]; //create array to hold number of rolls
 
        // loop through number of times you rolled
        for (int i = 0; i < diceRolls.length; i++) 
        {
            diceOne[i] = r.nextInt(numArr.length);
            diceTwo[i] = r.nextInt(numArr.length);
 
           totalDiceAmt = diceOne[i] + diceTwo[i];
 
           //  loop through number of times 2 was rolled
           if (totalDiceAmt == 2)
           {
               snakeEysRolled++;
           }
           //  loop through number of times 7 was rolled
           if (totalDiceAmt == 7 )
           {
               crapsRolled++;
           }
        }
 
        // print statement 
        System.out.println("Sneke Eyes was rolled " + snakeEysRolled + " times");
        // print blank line
        System.out.println();
        System.out.println("Craps was rolled " + crapsRolled + " times");
    } // end roll dice method
} // end Dice class

Review the tutorial on arrays: and understand the purpose for declaring arrays, initializing arrays, etc.

WOW. Thanks a million for pointing this out, I did not initialize diceOne and diceTwo arrays. After reading the tutorial it showed me what I was doing wrong. I was able to resolve this by adding:

int[] diceOne = new int[d]; // dice one variable
int[] diceTwo = new int[d]; // dice two variable

Thanks again.