CS 5 Fall 2009
Short Assignment #7
Due Friday, October 9

You want vice? You've got vice. We'll go for gambling. Craps, to be specific.

There are a few variations of craps, but let's focus on the simplest one, in which the player is what's known as a "right bettor." The game starts with what's called a "come-out roll," in which the player rolls a pair of dice. There are three possible results of the come-out roll:

• If the dice show a 2, 3, or 12, the player automatically loses.
• If the dice show a 7 or 11, the player automatically wins.
• Otherwise, the value shown on the dice (which must be a 4, 5, 6, 8, 9, or 10) is called the "point." The player repeatedly rolls the dice until one of two things happens:
  • If the roll has the same value as the point, the player wins.
  • If the roll is a 7, the player loses.

Your job is to help me write some Java code to play a game of craps. Download the files PlayCraps.java, CrapsPlayer.java, and Dice.java. (You can option-click on these links to download the files.) The PlayCraps and Dice classes are complete; you should make no changes to these. Your job is to write all the methods of the CrapsPlayer class.

The Dice class, which represents a pair of dice, has just two methods. The constructor creates a random number generator. The roll method returns the value obtained by generating two random numbers (thereby simulating rolling the two dice) and summing their results (after correcting for random numbers starting from 0).

The PlayCraps class has just a main method, which plays a game of craps. Other than System.out.println, the only methods that main calls are methods of the CrapsPlayer class. Once you understand the purpose of each of the CrapsPlayer methods, you should be able to see that the operation of main matches the rules of craps given above.

Let's look at the CrapsPlayer class. It has two instance variables:

• theDice represents the pair of dice.
• thePoint is the integer-valued point obtained on the come-out roll.

• The constructor needs to create the pair of dice (assigning to the instance variable theDice), and it needs to roll the dice to perform the come-out roll. The come-out roll assigns the value on the dice to thePoint. After the constructor creates the dice and performs the come-out roll, it announces the result of the come-out roll using a line of code that I have provided.

• isAutomaticLoser returns a boolean value that is true if the come-out roll is an automatic loser (a 2, 3, or 12), and false otherwise. (Remember where you stored the result of the come-out roll in the constructor.)

• isAutomaticWinner returns a boolean value that is true if the come-out roll is an automatic winner (a 7 or 11), and false otherwise.

• roll performs some roll that occurs after the come-out roll. It just returns the value rolled without changing the point.

• isWinner returns a boolean that is true if the value of the roll supplied as its parameter equals the point, and false otherwise.

None of the lines of code you write should call System.out.println or System.out.print. Notice also that this program requires no console input; all input comes from rolling the dice, which in turn comes from the random number generator.

Hand in a listing of your CrapsPlayer.java file, along with output from eight different runs of the program.

For your edification, here are five runs of my version:

1. The come-out roll is 7. You win!

2. The come-out roll is 9. You rolled a 8. You rolled a 2. You rolled a 8. You rolled a 5. You rolled a 2. You rolled a 6. You rolled a 8. You rolled a 4. You rolled a 9. You win!

3. The come-out roll is 8. You rolled a 6. You rolled a 2. You rolled a 7. You lose!

4. The come-out roll is 6. You rolled a 3. You rolled a 3. You rolled a 10. You rolled a 5. You rolled a 2. You rolled a 9. You rolled a 3. You rolled a 7. You lose!

5. The come-out roll is 3. You lose!

When you are done, please take a moment to look over how the three classes interact. Think about how I designed this program and why I might have made some of the design decisions that I made. You will have to make several design decisions in Lab Assignment 1, and understanding the design of this craps program can help you become a better designer.

You might be confused because the identifier roll appears in three different contexts:

• As a method of the Dice class, to return the value of a roll of the dice.
• As a method of the CrapsPlayer class, to return the value of a roll that occurs after the come-out roll.
• As a local variable in the main method of the PlayCraps class, to store the result of a roll that occurs after the come-out roll.

Looking at that line in full, we see roll = bettor.roll(), in which the identifier roll appears in two different contexts. As we've just seen, the rightmost appearance denotes the roll method of CrapsPlayer. What about the appearance of roll on the left-hand side? It's clearly not denoting a method: there are no parentheses (so it cannot be a call), and besides, you know that you have to have a variable on the left-hand side of an assignment. So it must denote the local variable roll in the main method.