java.lang.ArrayIndexOutOfBoundsException

[Marcus]

Hello, I am writing a program that plays 1000 games of craps then prints out win, loss, the amt of rolls for each game, the odds of winning and losing. I am getting the following error:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 22
at chapt7.Craps.play(Craps.java:94)
at chapt7.Craps.main(Craps.java:17)

I have been over this numerous times and can't seem to figure out the issue, here is my code.

package chapt7;

// Craps class simulates the dice game craps.
import java.util.Random;

public class Craps 
{
	public static void main(String[] args)
	{
		int whenWin[] = new int[22]; //array to store number of rolls that it takes to win each game
		 							 //whenWin[0] not used, more than 20 rolls counts is stored in whenWin[21]
		int whenLose[] = new int[22]; //array to store number of rolls that it takes to lose each game
									  //whenLose[0] not used, more than 20 rolls counts is stored in whenLose[21]
		
		//plays 1000 games of craps
		for (int i = 0; i < 1000; i++)
			play(whenWin, whenLose);
		//1000 games complete
		
		//prints out the amount of times game was won on the 'j'th roll
		for (int j = 1; j < 22; j++)
		{
			if (j == 21)
				System.out.printf("The amount of times won after roll %d is %d\n", j, whenWin[j]);
			else
				System.out.printf("The amount of times won on roll %d is %d\n", j, whenWin[j]);
		} //end for loop
		
		//prints out the amount of times game was lost on the 'j'th roll
		for (int j = 1; j < 22; j++)
		{
			if (j == 21)
				System.out.printf("The amount of times lost after roll %d is %d\n", j, whenLose[j]);
		
			else
				System.out.printf("The amount of times lost on roll %d is %d\n", j, whenLose[j]);
		} //end for loop
		
		chances(whenWin, whenLose); //caculates and prints out craps chances
		avgLengthGame(whenWin, whenLose); //calculates and prints out avg number of rolls/game
		
	}//end main
	
	
	// create random number generator for use in method rollDice
	private static Random randomNumbers = new Random(); 
  
	// enumeration with constants that represent the game status
	private enum Status { CONTINUE, WON, LOST };                
  
	// constants that represent common rolls of the dice
	private final static int SNAKE_EYES = 2;
	private final static int TREY = 3;      
	private final static int SEVEN = 7;     
	private final static int YO_LEVEN = 11; 
	private final static int BOX_CARS = 12; 
  
	// plays one game of craps
	public static void play(int[] whenWin, int[] whenLose)
	{
		int myPoint = 0; // point if no win or loss on first roll
		Status gameStatus; // can contain CONTINUE, WON or LOST
        int rollCount = 1; //counts # of rolls
        int sumOfDice = rollDice(); // first roll of the dice
        // determine game status and point based on first roll 
        switch ( sumOfDice ) 
        {
           case SEVEN: // win with 7 on first roll    
           case YO_LEVEN: // win with 11 on first roll
        	   gameStatus = Status.WON;
        	   whenWin[rollCount]++;
        	   break;
           case SNAKE_EYES: // lose with 2 on first roll
           case TREY: // lose with 3 on first roll      
           case BOX_CARS: // lose with 12 on first roll 
              gameStatus = Status.LOST;
              whenLose[rollCount]++;
              break;
           default: // did not win or lose, so remember point
              gameStatus = Status.CONTINUE; // game is not over
              myPoint = sumOfDice; // remember the point
              break; // optional at end of switch
        } // end switch 
  
        // while game is not complete
        while ( gameStatus == Status.CONTINUE ) // not WON or LOST
        { 
           sumOfDice = rollDice(); // roll dice again
           rollCount++;
           // determine game status
           if ( sumOfDice == myPoint ) // win by making point
           {
        	   		gameStatus = Status.WON;
        	   		whenWin[rollCount]++;
           }
           else
           {   
              if ( sumOfDice == SEVEN ) // lose by rolling 7 before point
              {	  
            	  	gameStatus = Status.LOST;
              		whenLose[rollCount]++;
              }
           }
        } // end while 
  
     } // end method play
  
     // roll dice, calculate sum and display results
     public static int rollDice()
     {
        // pick random die values
        int die1 = 1 + randomNumbers.nextInt( 6 ); // first die roll
        int die2 = 1 + randomNumbers.nextInt( 6 ); // second die roll
  
        int sum = die1 + die2; // sum of die values
        
        return sum; // return sum of dice
     } // end method rollDice
     
     //determines chances of wining craps
     public static int chances(int[] win, int[] lose)
     {
    	 int w = 0; //counts the number games won
    	 int l = 0; //counts the number games lost
    	 for (int i =1; i < 22; i++)
    	 {
    		 w = w + win[i];
    		 l = l + lose[l];
    	 }
    	 System.out.printf("The Chances of winning craps is %d:%d\n", w/w, l/w);
    	 return 0;	 
     }//end method chances
     
     //calculates the average length of each game, i.e. avg amt of rolls to win or lose
     public static int avgLengthGame(int[] win, int[] lose)
     {
    	 int numOfRolls = 0;
    	 int avg = 0;
    	 for (int i =1; i < 22; i++)
    	 {
    		 numOfRolls = numOfRolls + (win[i] * i) + (lose[i] * i);
    	 }
    	 avg = numOfRolls/1000;
    	 System.out.printf("The Average number of rolls per game is %d\n", avg);
    	 return 0;
     }//end method avgLengthGame
     
  } // end class Craps

I am using eclipse, if that is of any help? Thanks

Marcus:cool:

[Felissa]

You're problem is that you limit to the number of plays to 22. But it is very possible for you to play more then 22 times.

If you notice, sometimes you'll get the exception and sometimes you wont.

int whenWin[] = new int[22]

You can do one of three things. You can either increase the amount of the array to some extreme amount that makes no sense.
You can keep it at 22 length, but while you're going through your loop, check for the length and either stop playing or increase the size of the array. Or you can use an ArrayList, which will only give you size issues if you take up the amount of RAM in your computer.

My personal suggestion is to use an ArrayList.

Greetings
Felissa:p