CS 305j - Programming Project 5
Practice with: Conditional statements, loops, parameters and user input


For this project you will code a version of the rock, paper, scissors game. Your program will be stored in the file RockPaperScissors.java.

This assignment is a pair programming assignment. You may work with one other person on this project using the pair programming technique. (You are not required to work with a partner - you may work alone). Read the pair programming requirements on the course webpage carefully before beginning work on this assignment. You are allowed to work with anyone in the class - your partner does not need to be in your discussion section. If you work as part of a pair, only one solution will be submitted for the pair. Once you start the assignment, you cannot switch partners. If you do not want to work with a partner after starting the assignment, you must both complete the lab individually, and you must both email the instructor to explain why you are not completing the assignment as a pair. Failure to follow the pair programming rules (and include the neccessary additional documentation in your files) will result in significant point deductions on your project.


For this assignment you are limited to the language features in chapters 1 through 4 of the textbook.

Write a program to allow a human to play a game of Rock, Paper, Scissors versus the computer. Look at the sample output below which shows 2 sample runs from my solution to this problem. This shows you what the output of your program should be. (In the sample data the input from the user was their name, the number of rounds to play, and a choice for rock, paper, or scissors each round). The sample runs are shown in green to distinguish them from project requirements.

Sample Run:

Welcome to Rock Paper Scissors. I, the computer, will be your opponent.
Please type in your name and press return: Nathan

Welcome Nathan.
All right Nathan. How many games would you like to play?
Enter the number of rounds you want to play and press return: 9


Round 1.
Nathan, please enter your choice for this round.
1 for rock, 2 for paper, and 3 for scissors: 1
Computer picked rock, Nathan picked rock.

This round is a draw.


Round 2.
Nathan, please enter your choice for this round.
1 for rock, 2 for paper, and 3 for scissors: 2
Computer picked rock, Nathan picked paper.

Paper covers rock. You win.


Round 3.
Nathan, please enter your choice for this round.
1 for rock, 2 for paper, and 3 for scissors: 3
Computer picked rock, Nathan picked scissors.

Rock breaks scissors. I win.


Round 4.
Nathan, please enter your choice for this round.
1 for rock, 2 for paper, and 3 for scissors: 1
Computer picked paper, Nathan picked rock.

Paper covers rock. I win.


Round 5.
Nathan, please enter your choice for this round.
1 for rock, 2 for paper, and 3 for scissors: 2
Computer picked paper, Nathan picked paper.

This round is a draw.


Round 6.
Nathan, please enter your choice for this round.
1 for rock, 2 for paper, and 3 for scissors: 3
Computer picked paper, Nathan picked scissors.

Scissors cut paper. You win.


Round 7.
Nathan, please enter your choice for this round.
1 for rock, 2 for paper, and 3 for scissors: 1
Computer picked scissors, Nathan picked rock.

Rock breaks scissors. You win.


Round 8.
Nathan, please enter your choice for this round.
1 for rock, 2 for paper, and 3 for scissors: 2
Computer picked scissors, Nathan picked paper.

Scissors cut paper. I win.


Round 9.
Nathan, please enter your choice for this round.
1 for rock, 2 for paper, and 3 for scissors: 3
Computer picked scissors, Nathan picked scissors.

This round is a draw.


We played 9 games of Rock Paper Scissors.
The computer won 3 times.
Nathan won 3 times.
There were 3 draws.
We are evenly matched at this game.

Sample Run 2:

Welcome to Rock Paper Scissors. I, the computer, will be your opponent.
Please type in your name and press return: Lily

Welcome Lily.
All right Lily. How many games would you like to play?
Enter the number of rounds you want to play and press return: 7


Round 1.
Lily, please enter your choice for this round.
1 for rock, 2 for paper, and 3 for scissors: 1
Computer picked scissors, Lily picked rock.

Rock breaks scissors. You win.


Round 2.
Lily, please enter your choice for this round.
1 for rock, 2 for paper, and 3 for scissors: 1
Computer picked rock, Lily picked rock.

This round is a draw.


Round 3.
Lily, please enter your choice for this round.
1 for rock, 2 for paper, and 3 for scissors: 1
Computer picked rock, Lily picked rock.

This round is a draw.


Round 4.
Lily, please enter your choice for this round.
1 for rock, 2 for paper, and 3 for scissors: 1
Computer picked scissors, Lily picked rock.

Rock breaks scissors. You win.


Round 5.
Lily, please enter your choice for this round.
1 for rock, 2 for paper, and 3 for scissors: 3
Computer picked paper, Lily picked scissors.

Scissors cut paper. You win.


Round 6.
Lily, please enter your choice for this round.
1 for rock, 2 for paper, and 3 for scissors: 3
Computer picked scissors, Lily picked scissors.

This round is a draw.


Round 7.
Lily, please enter your choice for this round.
1 for rock, 2 for paper, and 3 for scissors: 2
Computer picked paper, Lily picked paper.

This round is a draw.


We played 7 games of Rock Paper Scissors.
The computer won 0 times.
Lily won 3 times.
There were 4 draws.
You are a master at Rock, Paper, Scissors.


The program should:

This is not an easy program, mostly due to the size of the program. The individual steps are not too difficult, but there are quite a few steps!! The program description above gives you a rough idea of how to break the program up into parts.

Approach the problem is steps as we have done in class. Have a high level structure and then implement parts of that structure (the individual methods) one at a time, testing to make sure they work before going on. You may have to write some testing code that will not be part of the final program. Write psuedocode before you start writing Java code!

Here are some tips on the various parts of the program.

1. main method. In the main program declare a Scanner variable that is hooked up to System.in. You need to include the line of code

import java.util.*;

at the top of your program. Pass the Scanner object you create as a parameter to any methods that need it. The main method should not have a lot of statements, instead it will be calling other methods.

2. ask the user for their name. This is a good candidate for a separate method that returns a String.

3. ask the user how many rounds of Rock, Paper, Scissors they want to play. This is another good candidate for a separate method that returns an int. You do not have to do any error checking on the user input. If they enter something that is not an int it is appropriate for the program to end due to a runtime error.

Recall that if you use the nextInt() method from the Scanner class you will have to call the nextLine() method after that to advance the Scanner past the end of line character. The nextInt() method does not advance past the end of line character.

4. playing the rounds of the game Given our current programming tools this will be the largest and most complex method. It is in turn broken down into several parts. You will need a number of local variables in this method and they should be declared at the top of the method. Obviously you will need a loop to play the appropriate number of rounds.

5. ask the user what their choice is. The user will enter an integer as their choice. You do not need to error check their input. Recall that if you use the nextInt() method from the Scanner class you will have to call the nextLine() method after that to advance the Scanner past the end of line character. The nextInt() method does not advance past the end of line character.

6. have the computer make a random choice. To do this you need the computer to pick a random number between 1 and 3. Create a Random object and then call nextInt() on that Random object repeatedly to produce the random numbers.

7. print out each player's choice. You will find it useful to have a method that is passed an  int parameters and returns the correct String for that int. In this program 1 represents "Rock", 2 represents "Paper", and 3 represents "Scissors".

8. print the results of that round. This is the most algorithmically difficult part of the assignment because their are nine possible outcomes and using the programming tools of chapters 1 - 4 it is difficult to remove redundancy. The nine possible outcomes are

Computer Choice Human Choice Result
Rock Rock Draw
Rock Paper Human Wins
Rock Scissors Computer Wins
Paper Rock Computer Wins
Paper Paper Draw
Paper Scissors Human Wins
Scissors Rock Human Wins
Scissors Paper Computer Wins
Scissors Scissors Draw

You can eliminate some redundancy with these nine outcomes, but not much.

9. after playing the specified number of rounds display how time the user won, how many times the computer won, and how many draws occurred.   The method that runs the rounds should call a method to display this information.

10. declare who the better player was based on the number of wins.  This can be part of the results method but will again require some conditional execution with if statements.

11. Use class constants for the integers representing rock, paper, and scissors. Recall class constants are declared at the top of the class outside any methods:

public static final int ROCK = 1;

Style issues. Not only will we be grading whether your program works, but does it have good style. Did you provide a good structure to the program using static methods? Did you use meaningful identifiers? Did you provide consistent tabbing and spacing for code inside loops and if statements? Did you provide comments for you methods and your code?

Extras: If you are looking to do something extra and interesting on this project, consider make modifications to how the computer makes its choice. If the human opponent is truly making random guesses than making random guesses is the best computer strategy. It turns out is very hard for people to make truly random guesses. They fall into tendencies. For example people will often will make a choice different than the one they last made. An interesting approach would be to try a different computer picking algorithm. For example what if the computer looks at a human's last guess and assumes they won't make that guess for this round. How could the computer make its choice to increase its chances of winning using this strategy?

When finished turn in your RockPaperScissors.java program using the turnin program. If you are working with another person turn the assignment in to only one person's account, but ensure the header is filled in with both of your names and the unique class ID for your sections.