Java Rock / Paper/ Scissors, doing this wrong?

Question

Learning java obviously. I was able to make the game work fine. But I need to make it so that if the user puts something other than R/P/S then it defaults to Rock. I don't need to loop. The game works perfect if I put rock. If I put anything other than RPS it also works perfect and defaults to rock. If, however, I do Paper or Scissors, it gives me the paper and scissors answer, AND the defaults to rock answer. Any hints on why this isn't working?

Also, is my direction wrong? Could I be doing this a better way? This feels really... unelegant at best.

    public static void main(String[] args) {
            // TODO Auto-generated method stub
    Scanner in = new Scanner(System.in);
    String userChoice="", userInput, compChoice="";
    int ranInt = (int)(Math.random()*3);
    if (ranInt == 0){
            compChoice = "Rock";
    } else if (ranInt == 1){
            compChoice = "Paper";
    }else if (ranInt == 2){
            compChoice = "Scissors";
    }
    System.out.println("Please select one of [R/P/S]: ");
            userInput = in.next();

    if(userInput.equalsIgnoreCase("p")){
            userChoice = "Paper ";
            if(compChoice.equalsIgnoreCase("Rock")){
                    System.out.println("You chose: "+userChoice);
                    System.out.println("I chose: "+compChoice);
                    System.out.println(userChoice + "beats "+compChoice +"- you win!");
            }else if (compChoice.equalsIgnoreCase("Paper")){
                    System.out.println("You chose: "+userChoice);
                    System.out.println("I chose: "+compChoice);
                    System.out.println("A tie!");
            }else if(compChoice.equalsIgnoreCase("Scissors")){
                    System.out.println("You chose: "+userChoice);
                    System.out.println("I chose: "+compChoice);
                    System.out.println(compChoice + " beats " + userChoice + " - i win!");
                    }
            }

    if(userInput.equalsIgnoreCase("S")){
            userChoice = "Scissors ";
            if(compChoice.equalsIgnoreCase("Paper")){
                    System.out.println("You chose: "+userChoice);
                    System.out.println("I choce: "+compChoice);
                    System.out.println(userChoice + "beats "+compChoice +"- you win!");
            }else if(compChoice.equalsIgnoreCase("Scissors")){
                    System.out.println("You chose: "+userChoice);
                    System.out.println("I chose: "+compChoice);
                    System.out.println("A tie!");
            }else if(compChoice.equalsIgnoreCase("Rock")){
                    System.out.println("You chose: "+userChoice);
                    System.out.println("I chose: "+compChoice);
                    System.out.println(compChoice + " beats " + userChoice + " - i win!");
                    }
            }              
    if(userInput.equalsIgnoreCase("R")){
            userChoice = "Rock ";
            if(compChoice.equalsIgnoreCase("Rock")){
                    System.out.println("You chose: "+userChoice);
                    System.out.println("I chose: "+compChoice);
                    System.out.println("A Tie!");
            }else if(compChoice.equalsIgnoreCase("Paper")){
                    System.out.println("You chose: "+userChoice);
                    System.out.println("I chose: "+compChoice);
                    System.out.println(compChoice + " beats " + userChoice + " - you lose!");
            }else if(compChoice.equalsIgnoreCase("Scissors")){
                    System.out.println("You chose: "+userChoice);
                    System.out.println("I chose: "+compChoice);
                    System.out.println(userChoice + " beats " + compChoice + " - you win!");
                    }
            }
    else {
            userChoice = "";
            System.out.println("Invalid selection, defaulting to rock.");
            if(compChoice.equalsIgnoreCase("Rock")){
                    System.out.println("You chose: Rock");
                    System.out.println("I chose: "+compChoice);
                    System.out.println("A Tie!");
            }else if (compChoice.equalsIgnoreCase("Paper")){
                    System.out.println("You chose: Rock");
                    System.out.println("I chose: "+compChoice);
                    System.out.println(compChoice + " beats " + "Rock - you lose!");
            } else if(compChoice.equalsIgnoreCase("Scissors")){
                    System.out.println("You chose: Rock");
                    System.out.println("I chose: "+compChoice);
                    System.out.println("Rock beats " + compChoice + " - you win!");
                    } 
            }
    }

}

Answer 1

Your code needs to have else if for the 'S' branch and the 'R' branch, otherwise the logic proceeds as follows (for an 'S' input):

if (P) do something // No, so move on
if (S) do something // Yes, so do 'S' stuff
if (R) do something else do something different // Not 'R', so doing something different.

For ideas on adding 'elegance' to your code, check out the Rosetta Code page for Rock, Paper, Scissors

Answer 2

You asked about "elegant" solution, and one way to do this is to use a win matrix, in other words something like so:

public enum RPS {
   ROCK, PAPER, SCISSORS;

   public int test(RPS otherRps) {
      int[][] winMatrix = { 
            {  0, -1,  1 }, 
            {  1,  0, -1 }, 
            { -1,  1,  0 } };
      return winMatrix[ordinal()][otherRps.ordinal()];
   }
}

Then you could test the result by simply calling the enum's test(...) method. For example:

import java.util.Random;
import java.util.Scanner;

public class RockPaperScissors {
   private static Random random = new Random();
   private static Scanner in = new Scanner(System.in);

   public static void main(String[] args) {
      RPS compChoice = RPS.values()[random.nextInt(RPS.values().length)];
      RPS userChoice = getUserChoice();

      String result = "";
      switch (userChoice.test(compChoice)) {
      case 1:
         result = "you win!";
         break;

      case -1:
         result = "you lose!";
         break;

      case 0:
         result = "it's a tie";

      default:
         break;
      }
      System.out.printf("You chose %s, the computer chose %s, %s%n",
            userChoice, compChoice, result);
   }

   private static RPS getUserChoice() {
      System.out.print("Please select one of [R/P/S]: ");
      String userChoiceStr = in.nextLine().trim();
      if (userChoiceStr.isEmpty()) {
         return RPS.ROCK;
      }
      for (RPS rps : RPS.values()) {
         if (rps.toString().startsWith(userChoiceStr.toUpperCase())) {
            return rps;
         }
      }

      return RPS.ROCK; // default
   }
}

Answer 3

In pseudocode, the structure of your code is:

if (paper) {
    process paper
}

if (scissors) {
    process scissors
}

if (rock) {
    process rock
} else {
    process default rock
}

Note that (since the cases are mutually exclusive) if paper or scissors is true, then rock is false and the else will execute. Just change the structure to:

if (paper) {
    process paper
} else if (scissors) {
    process scissors
} else if (rock) {
    process rock
} else {
    process default rock
}