Rock, Paper, Scissors is a hand game played by two people. Both people would say "rock, paper, scissors" and then simultaneously form one of three objects (rock, paper, or scissors) with an outstretched hand. The winner is determined by the hand formations. Scissors beats paper, paper beats rock, and rock beats scissors. If both players play the same hand formation, it is considered a tie. We will write a simple game in Java to simulates Rock, Paper, Scissors where one player is the user and the other player is the computer.

Steps

  1. This will be the class where we will write the game. You may choose to name it something else such as Game or Main . Write in method declarations for the constructor and the main method.
     public 
     class 
     RockPaperScissors 
     { 
     public 
     RockPaperScissors 
     () 
     { 
     } 
     public 
     static 
     void 
     main 
     ( 
     String 
     [] 
     args 
     ) 
     { 
     } 
     } 
    
  2. We could use strings to represent rock, paper, or scissors, but an enumeration allows us to predefine our constants which means that using the enumeration is a better design. We will call our enum type Move with the values ROCK , PAPER , and SCISSORS .
     private 
     enum 
     Move 
     { 
     ROCK 
     , 
     PAPER 
     , 
     SCISSORS 
     } 
    
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  3. These classes will represent our players in the game. You may choose to make these classes public. The User class will be the class that prompts the user for either rock, paper, or scissors, so we will need to write a getMove() method. The Computer class will also need to have a getMove() method so that the computer can also make a move. We will put placeholders in these methods and implement them later. The User class will require a constructor that sets up the Scanner object to take in the user input. We will put the Scanner as a private field for the user and then initiate it in the constructor. Since we are using the Scanner class, we need to write an import statement for it at the top of our code. The Computer class does not require a constructor, so we do not need to write one; when we initiate the Computer object, we will just be calling the default constructor. Here is what our RockPaperScissors class looks like now:
     import 
     java.util.Scanner 
     ; 
     public 
     class 
     RockPaperScissors 
     { 
     private 
     enum 
     Move 
     { 
     ROCK 
     , 
     PAPER 
     , 
     SCISSORS 
     } 
     private 
     class 
     User 
     { 
     private 
     Scanner 
     inputScanner 
     ; 
     public 
     User 
     () 
     { 
     inputScanner 
     = 
     new 
     Scanner 
     ( 
     System 
     . 
     in 
     ); 
     } 
     public 
     Move 
     getMove 
     () 
     { 
     // TODO: Implement this method 
     return 
     null 
     ; 
     } 
     } 
     private 
     class 
     Computer 
     { 
     public 
     Move 
     getMove 
     () 
     { 
     // TODO: Implement this method 
     return 
     null 
     ; 
     } 
     } 
     public 
     RockPaperScissors 
     () 
     { 
     } 
     public 
     static 
     void 
     main 
     ( 
     String 
     [] 
     args 
     ) 
     { 
     } 
     } 
    
  4. This method will return a random Move . We can get an array of Move enumerations by calling the values() method: Move.values() . To choose a random Move enumeration in this values array, we need to generate a random index that is an integer between 0 and the length of our values array. To do this, we can use the nextInt() method of the Random class which we need to import from java.util . After we have gotten the random index, we can return the Move of that index from our values array.
     public 
     Move 
     getMove 
     () 
     { 
     Move 
     [] 
     moves 
     = 
     Move 
     . 
     values 
     (); 
     Random 
     random 
     = 
     new 
     Random 
     (); 
     int 
     index 
     = 
     random 
     . 
     nextInt 
     ( 
     moves 
     . 
     length 
     ); 
     return 
     moves 
     [ 
     index 
     ]; 
     } 
    
  5. This method will return a Move corresponding to what the user has input. We will expect the user to write either "rock", "paper", or "scissors". First, we need to prompt the user for an input: System.out.print("Rock, paper, or scissors? ") . Then use the nextLine() method of the Scanner object to get the user input as a string. We need now need to check if the user has submitted a valid move, but we can be lenient if the user has misspelled a word. So we will only check if the first letter of the user input is either "R" (for rock), "P" (for paper), or "S" (for scissors), and we won't care about the case because we will first use the toUpperCase() method of the String class to make the user input string all uppercase. If the user has not entered a remotely correct input, we will prompt the user again. Then, depending on what the user has put in, we will return a corresponding move.
     public 
     Move 
     getMove 
     () 
     { 
     // Prompt the user 
     System 
     . 
     out 
     . 
     print 
     ( 
     "Rock, paper, or scissors? " 
     ); 
     // Get the user input 
     String 
     userInput 
     = 
     inputScanner 
     . 
     nextLine 
     (); 
     userInput 
     = 
     userInput 
     . 
     toUpperCase 
     (); 
     char 
     firstLetter 
     = 
     userInput 
     . 
     charAt 
     ( 
     0 
     ); 
     if 
     ( 
     firstLetter 
     == 
     'R' 
     || 
     firstLetter 
     == 
     'P' 
     || 
     firstLetter 
     == 
     'S' 
     ) 
     { 
     // User has entered a valid input 
     switch 
     ( 
     firstLetter 
     ) 
     { 
     case 
     'R' 
     : 
     return 
     Move 
     . 
     ROCK 
     ; 
     case 
     'P' 
     : 
     return 
     Move 
     . 
     PAPER 
     ; 
     case 
     'S' 
     : 
     return 
     Move 
     . 
     SCISSORS 
     ; 
     } 
     } 
     // User has not entered a valid input. Prompt again. 
     return 
     getMove 
     (); 
     } 
    
  6. The user should be able to play the game over and over again. In order to determine whether the user wants to play again, we need to write a playAgain() method that returns a boolean telling the game whether the user has determined to play again or not. In this method, we are using the Scanner that we had previously initiated in the constructor to get a "Yes" or a "No" from the user. We will only check if the first letter is 'Y' to determine whether the user wants to play again. Any other input will mean that the user does not want to play again.
     public 
     boolean 
     playAgain 
     () 
     { 
     System 
     . 
     out 
     . 
     print 
     ( 
     "Do you want to play again? " 
     ); 
     String 
     userInput 
     = 
     inputScanner 
     . 
     nextLine 
     (); 
     userInput 
     = 
     userInput 
     . 
     toUpperCase 
     (); 
     return 
     userInput 
     . 
     charAt 
     ( 
     0 
     ) 
     == 
     'Y' 
     ; 
     } 
    
  7. Now that we have finished writing the User and Computer classes, we can focus on working on our actual game. Create private fields for the User and Computer classes in the RockPaperScissors class. We will need to access these fields to access the getMove() methods when we're playing the game. In the constructor for the RockPaperScissors class, initiate these fields. We will also need to keep track of the score in userScore and computerScore fields, which we need to initiate as 0 in the constructor. We need to keep track of the number of games as well, which will also be a field initiated as 0.
     private 
     User 
     user 
     ; 
     private 
     Computer 
     computer 
     ; 
     private 
     int 
     userScore 
     ; 
     private 
     int 
     computerScore 
     ; 
     private 
     int 
     numberOfGames 
     ; 
     public 
     RockPaperScissors 
     () 
     { 
     user 
     = 
     new 
     User 
     (); 
     computer 
     = 
     new 
     Computer 
     (); 
     userScore 
     = 
     0 
     ; 
     computerScore 
     = 
     0 
     ; 
     numberOfGames 
     = 
     0 
     ; 
     } 
    
  8. We need to write a compareMoves() method that returns 0 if the moves are the same, 1 if the current move beats the other move, and -1 if the current move loses to the other move. This will be useful for determining the winner in the game. To implement this method, we will first return 0 if the moves are the same and therefore we have a tie. Then write a switch statement for returning 1 or -1.
     private 
     enum 
     Move 
     { 
     ROCK 
     , 
     PAPER 
     , 
     SCISSORS 
     ; 
     /** 
     * Compares this move with another move to determining a tie, a win, or 
     * a loss. 
     * 
     * @param otherMove 
     *            move to compare to 
     * @return 1 if this move beats the other move, -1 if this move loses to 
     *         the other move, 0 if these moves tie 
     */ 
     public 
     int 
     compareMoves 
     ( 
     Move 
     otherMove 
     ) 
     { 
     // Tie 
     if 
     ( 
     this 
     == 
     otherMove 
     ) 
     return 
     0 
     ; 
     switch 
     ( 
     this 
     ) 
     { 
     case 
     ROCK 
     : 
     return 
     ( 
     otherMove 
     == 
     SCISSORS 
     ? 
     1 
     : 
     - 
     1 
     ); 
     case 
     PAPER 
     : 
     return 
     ( 
     otherMove 
     == 
     ROCK 
     ? 
     1 
     : 
     - 
     1 
     ); 
     case 
     SCISSORS 
     : 
     return 
     ( 
     otherMove 
     == 
     PAPER 
     ? 
     1 
     : 
     - 
     1 
     ); 
     } 
     // Should never reach here 
     return 
     0 
     ; 
     } 
     } 
    
  9. This method will be the playing of the game. Start out by putting a simple System.out.println in the method.
     public 
     void 
     startGame 
     () 
     { 
     System 
     . 
     out 
     . 
     println 
     ( 
     "ROCK, PAPER, SCISSORS!" 
     ); 
     } 
    
  10. In the startGame() method, use the getMove() methods from the User class and the Computer class to get the user and the computer's moves.
     Move 
     userMove 
     = 
     user 
     . 
     getMove 
     (); 
     Move 
     computerMove 
     = 
     computer 
     . 
     getMove 
     (); 
     System 
     . 
     out 
     . 
     println 
     ( 
     "\nYou played " 
     + 
     userMove 
     + 
     "." 
     ); 
     System 
     . 
     out 
     . 
     println 
     ( 
     "Computer played " 
     + 
     computerMove 
     + 
     ".\n" 
     ); 
    
  11. Use the compareMoves() method from the Move enum to to determine whether the user won or not. If the user won, increment the user score by 1. If the user lost, increment the computer score by 1. If there was a tie, do not increment any of the scores. Then increment the number of games played by one.
     int 
     compareMoves 
     = 
     userMove 
     . 
     compareMoves 
     ( 
     computerMove 
     ); 
     switch 
     ( 
     compareMoves 
     ) 
     { 
     case 
     0 
     : 
     // Tie 
     System 
     . 
     out 
     . 
     println 
     ( 
     "Tie!" 
     ); 
     break 
     ; 
     case 
     1 
     : 
     // User wins 
     System 
     . 
     out 
     . 
     println 
     ( 
     userMove 
     + 
     " beats " 
     + 
     computerMove 
     + 
     ". You won!" 
     ); 
     userScore 
     ++; 
     break 
     ; 
     case 
     - 
     1 
     : 
     // Computer wins 
     System 
     . 
     out 
     . 
     println 
     ( 
     computerMove 
     + 
     " beats " 
     + 
     userMove 
     + 
     ". You lost." 
     ); 
     computerScore 
     ++; 
     break 
     ; 
     } 
     numberOfGames 
     ++; 
    
  12. If the user wants to play again, call startGame() again. Otherwise, call printGameStats() which will print out the statistics of the game. We will write this method in the next step.
     if 
     ( 
     user 
     . 
     playAgain 
     ()) 
     { 
     System 
     . 
     out 
     . 
     println 
     (); 
     startGame 
     (); 
     } 
     else 
     { 
     printGameStats 
     (); 
     } 
    
  13. This method will display the statistics of the game: number of wins, number of losses, number of ties, number of games played, and percentage of games won by the user. The percentage of games won is calculated by the (# wins + (# ties/2))/(# games played). This method uses System.out.printf to print out formatted text.
     private 
     void 
     printGameStats 
     () 
     { 
     int 
     wins 
     = 
     userScore 
     ; 
     int 
     losses 
     = 
     computerScore 
     ; 
     int 
     ties 
     = 
     numberOfGames 
     - 
     userScore 
     - 
     computerScore 
     ; 
     double 
     percentageWon 
     = 
     ( 
     wins 
     + 
     (( 
     double 
     ) 
     ties 
     ) 
     / 
     2 
     ) 
     / 
     numberOfGames 
     ; 
     // Line 
     System 
     . 
     out 
     . 
     print 
     ( 
     "+" 
     ); 
     printDashes 
     ( 
     68 
     ); 
     System 
     . 
     out 
     . 
     println 
     ( 
     "+" 
     ); 
     // Print titles 
     System 
     . 
     out 
     . 
     printf 
     ( 
     "|  %6s  |  %6s  |  %6s  |  %12s  |  %14s  |\n" 
     , 
     "WINS" 
     , 
     "LOSSES" 
     , 
     "TIES" 
     , 
     "GAMES PLAYED" 
     , 
     "PERCENTAGE WON" 
     ); 
     // Line 
     System 
     . 
     out 
     . 
     print 
     ( 
     "|" 
     ); 
     printDashes 
     ( 
     10 
     ); 
     System 
     . 
     out 
     . 
     print 
     ( 
     "+" 
     ); 
     printDashes 
     ( 
     10 
     ); 
     System 
     . 
     out 
     . 
     print 
     ( 
     "+" 
     ); 
     printDashes 
     ( 
     10 
     ); 
     System 
     . 
     out 
     . 
     print 
     ( 
     "+" 
     ); 
     printDashes 
     ( 
     16 
     ); 
     System 
     . 
     out 
     . 
     print 
     ( 
     "+" 
     ); 
     printDashes 
     ( 
     18 
     ); 
     System 
     . 
     out 
     . 
     println 
     ( 
     "|" 
     ); 
     // Print values 
     System 
     . 
     out 
     . 
     printf 
     ( 
     "|  %6d  |  %6d  |  %6d  |  %12d  |  %13.2f%%  |\n" 
     , 
     wins 
     , 
     losses 
     , 
     ties 
     , 
     numberOfGames 
     , 
     percentageWon 
     * 
     100 
     ); 
     // Line 
     System 
     . 
     out 
     . 
     print 
     ( 
     "+" 
     ); 
     printDashes 
     ( 
     68 
     ); 
     System 
     . 
     out 
     . 
     println 
     ( 
     "+" 
     ); 
     } 
    
  14. In the main class, initialize an instance of the RockPaperScissors class and call the startGame() method.
     public 
     static 
     void 
     main 
     ( 
     String 
     [] 
     args 
     ) 
     { 
     RockPaperScissors 
     game 
     = 
     new 
     RockPaperScissors 
     (); 
     game 
     . 
     startGame 
     (); 
     } 
    
  15. Now that we have gone through all the effort of writing the Rock, Paper, Scissors game, it's time to compile and test everything out!
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      Sample Program

       import 
       java.util.Random 
       ; 
       import 
       java.util.Scanner 
       ; 
       public 
       class 
       RockPaperScissors 
       { 
       private 
       User 
       user 
       ; 
       private 
       Computer 
       computer 
       ; 
       private 
       int 
       userScore 
       ; 
       private 
       int 
       computerScore 
       ; 
       private 
       int 
       numberOfGames 
       ; 
       private 
       enum 
       Move 
       { 
       ROCK 
       , 
       PAPER 
       , 
       SCISSORS 
       ; 
       /** 
       * Compares this move with another move to determining a tie, a win, or 
       * a loss. 
       * 
       * @param otherMove 
       *            move to compare to 
       * @return 1 if this move beats the other move, -1 if this move loses to 
       *         the other move, 0 if these moves tie 
       */ 
       public 
       int 
       compareMoves 
       ( 
       Move 
       otherMove 
       ) 
       { 
       // Tie 
       if 
       ( 
       this 
       == 
       otherMove 
       ) 
       return 
       0 
       ; 
       switch 
       ( 
       this 
       ) 
       { 
       case 
       ROCK 
       : 
       return 
       ( 
       otherMove 
       == 
       SCISSORS 
       ? 
       1 
       : 
       - 
       1 
       ); 
       case 
       PAPER 
       : 
       return 
       ( 
       otherMove 
       == 
       ROCK 
       ? 
       1 
       : 
       - 
       1 
       ); 
       case 
       SCISSORS 
       : 
       return 
       ( 
       otherMove 
       == 
       PAPER 
       ? 
       1 
       : 
       - 
       1 
       ); 
       } 
       // Should never reach here 
       return 
       0 
       ; 
       } 
       } 
       private 
       class 
       User 
       { 
       private 
       Scanner 
       inputScanner 
       ; 
       public 
       User 
       () 
       { 
       inputScanner 
       = 
       new 
       Scanner 
       ( 
       System 
       . 
       in 
       ); 
       } 
       public 
       Move 
       getMove 
       () 
       { 
       // Prompt the user 
       System 
       . 
       out 
       . 
       print 
       ( 
       "Rock, paper, or scissors? " 
       ); 
       // Get the user input 
       String 
       userInput 
       = 
       inputScanner 
       . 
       nextLine 
       (); 
       userInput 
       = 
       userInput 
       . 
       toUpperCase 
       (); 
       char 
       firstLetter 
       = 
       userInput 
       . 
       charAt 
       ( 
       0 
       ); 
       if 
       ( 
       firstLetter 
       == 
       'R' 
       || 
       firstLetter 
       == 
       'P' 
       || 
       firstLetter 
       == 
       'S' 
       ) 
       { 
       // User has entered a valid input 
       switch 
       ( 
       firstLetter 
       ) 
       { 
       case 
       'R' 
       : 
       return 
       Move 
       . 
       ROCK 
       ; 
       case 
       'P' 
       : 
       return 
       Move 
       . 
       PAPER 
       ; 
       case 
       'S' 
       : 
       return 
       Move 
       . 
       SCISSORS 
       ; 
       } 
       } 
       // User has not entered a valid input. Prompt again. 
       return 
       getMove 
       (); 
       } 
       public 
       boolean 
       playAgain 
       () 
       { 
       System 
       . 
       out 
       . 
       print 
       ( 
       "Do you want to play again? " 
       ); 
       String 
       userInput 
       = 
       inputScanner 
       . 
       nextLine 
       (); 
       userInput 
       = 
       userInput 
       . 
       toUpperCase 
       (); 
       return 
       userInput 
       . 
       charAt 
       ( 
       0 
       ) 
       == 
       'Y' 
       ; 
       } 
       } 
       private 
       class 
       Computer 
       { 
       public 
       Move 
       getMove 
       () 
       { 
       Move 
       [] 
       moves 
       = 
       Move 
       . 
       values 
       (); 
       Random 
       random 
       = 
       new 
       Random 
       (); 
       int 
       index 
       = 
       random 
       . 
       nextInt 
       ( 
       moves 
       . 
       length 
       ); 
       return 
       moves 
       [ 
       index 
       ]; 
       } 
       } 
       public 
       RockPaperScissors 
       () 
       { 
       user 
       = 
       new 
       User 
       (); 
       computer 
       = 
       new 
       Computer 
       (); 
       userScore 
       = 
       0 
       ; 
       computerScore 
       = 
       0 
       ; 
       numberOfGames 
       = 
       0 
       ; 
       } 
       public 
       void 
       startGame 
       () 
       { 
       System 
       . 
       out 
       . 
       println 
       ( 
       "ROCK, PAPER, SCISSORS!" 
       ); 
       // Get moves 
       Move 
       userMove 
       = 
       user 
       . 
       getMove 
       (); 
       Move 
       computerMove 
       = 
       computer 
       . 
       getMove 
       (); 
       System 
       . 
       out 
       . 
       println 
       ( 
       "\nYou played " 
       + 
       userMove 
       + 
       "." 
       ); 
       System 
       . 
       out 
       . 
       println 
       ( 
       "Computer played " 
       + 
       computerMove 
       + 
       ".\n" 
       ); 
       // Compare moves and determine winner 
       int 
       compareMoves 
       = 
       userMove 
       . 
       compareMoves 
       ( 
       computerMove 
       ); 
       switch 
       ( 
       compareMoves 
       ) 
       { 
       case 
       0 
       : 
       // Tie 
       System 
       . 
       out 
       . 
       println 
       ( 
       "Tie!" 
       ); 
       break 
       ; 
       case 
       1 
       : 
       // User wins 
       System 
       . 
       out 
       . 
       println 
       ( 
       userMove 
       + 
       " beats " 
       + 
       computerMove 
       + 
       ". You won!" 
       ); 
       userScore 
       ++; 
       break 
       ; 
       case 
       - 
       1 
       : 
       // Computer wins 
       System 
       . 
       out 
       . 
       println 
       ( 
       computerMove 
       + 
       " beats " 
       + 
       userMove 
       + 
       ". You lost." 
       ); 
       computerScore 
       ++; 
       break 
       ; 
       } 
       numberOfGames 
       ++; 
       // Ask the user to play again 
       if 
       ( 
       user 
       . 
       playAgain 
       ()) 
       { 
       System 
       . 
       out 
       . 
       println 
       (); 
       startGame 
       (); 
       } 
       else 
       { 
       printGameStats 
       (); 
       } 
       } 
       /** 
       * Prints out the statistics of the game. Calculates ties as 1/2 a win in 
       * percentage won. 
       */ 
       private 
       void 
       printGameStats 
       () 
       { 
       int 
       wins 
       = 
       userScore 
       ; 
       int 
       losses 
       = 
       computerScore 
       ; 
       int 
       ties 
       = 
       numberOfGames 
       - 
       userScore 
       - 
       computerScore 
       ; 
       double 
       percentageWon 
       = 
       ( 
       wins 
       + 
       (( 
       double 
       ) 
       ties 
       ) 
       / 
       2 
       ) 
       / 
       numberOfGames 
       ; 
       // Line 
       System 
       . 
       out 
       . 
       print 
       ( 
       "+" 
       ); 
       printDashes 
       ( 
       68 
       ); 
       System 
       . 
       out 
       . 
       println 
       ( 
       "+" 
       ); 
       // Print titles 
       System 
       . 
       out 
       . 
       printf 
       ( 
       "|  %6s  |  %6s  |  %6s  |  %12s  |  %14s  |\n" 
       , 
       "WINS" 
       , 
       "LOSSES" 
       , 
       "TIES" 
       , 
       "GAMES PLAYED" 
       , 
       "PERCENTAGE WON" 
       ); 
       // Line 
       System 
       . 
       out 
       . 
       print 
       ( 
       "|" 
       ); 
       printDashes 
       ( 
       10 
       ); 
       System 
       . 
       out 
       . 
       print 
       ( 
       "+" 
       ); 
       printDashes 
       ( 
       10 
       ); 
       System 
       . 
       out 
       . 
       print 
       ( 
       "+" 
       ); 
       printDashes 
       ( 
       10 
       ); 
       System 
       . 
       out 
       . 
       print 
       ( 
       "+" 
       ); 
       printDashes 
       ( 
       16 
       ); 
       System 
       . 
       out 
       . 
       print 
       ( 
       "+" 
       ); 
       printDashes 
       ( 
       18 
       ); 
       System 
       . 
       out 
       . 
       println 
       ( 
       "|" 
       ); 
       // Print values 
       System 
       . 
       out 
       . 
       printf 
       ( 
       "|  %6d  |  %6d  |  %6d  |  %12d  |  %13.2f%%  |\n" 
       , 
       wins 
       , 
       losses 
       , 
       ties 
       , 
       numberOfGames 
       , 
       percentageWon 
       * 
       100 
       ); 
       // Line 
       System 
       . 
       out 
       . 
       print 
       ( 
       "+" 
       ); 
       printDashes 
       ( 
       68 
       ); 
       System 
       . 
       out 
       . 
       println 
       ( 
       "+" 
       ); 
       } 
       private 
       void 
       printDashes 
       ( 
       int 
       numberOfDashes 
       ) 
       { 
       for 
       ( 
       int 
       i 
       = 
       0 
       ; 
       i 
       < 
       numberOfDashes 
       ; 
       i 
       ++) 
       { 
       System 
       . 
       out 
       . 
       print 
       ( 
       "-" 
       ); 
       } 
       } 
       public 
       static 
       void 
       main 
       ( 
       String 
       [] 
       args 
       ) 
       { 
       RockPaperScissors 
       game 
       = 
       new 
       RockPaperScissors 
       (); 
       game 
       . 
       startGame 
       (); 
       } 
       } 
      

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