Java - 嵌套While循环

Question

Greetings Stack Overflow users, I come to you this evening for assistance on a Java program that I have created. I'm relatively new to Java so please excuse my ignorance on the topic. I have made a Java program that's a "Rock" "Paper" "Scissors" game and there seems to be an error in one of the statements.

import java.util.Scanner;

public class TheAntlers {
public static void main(String[] args) {

    int playerHumanWins = 0;
    int playerComputerWins = 0;
    int numberOfTies = 0;
    int computerResult;

    Scanner input = new Scanner(System.in);

    while(true) {

        String startGame;
        String playerHuman;
        String playerComputer = " ";

        System.out.print("Do you want to play \"Rock\", \"Paper\", \"Scissors\"? (Y/N): ");
        startGame = input.nextLine();

        startGame = startGame.toUpperCase();

        if(startGame.equals("N")) {
            System.out.println("NO!");
            break;
        }
        else if(! startGame.equals("Y")) {
            startGame = startGame.toLowerCase();
            System.out.println("Sorry, " + startGame + " is not a valid entry...");               
        }
        while(startGame.equals("Y")) {
            System.out.print("Please choose \"Rock\", \"Paper\", or \"Scissors\": ");
            playerHuman = input.nextLine();

            computerResult = (int)(Math.random() * 3);

            playerHuman = playerHuman.toUpperCase();

            if(computerResult == 1) {
                playerComputer = "ROCK";
            }
            else if(computerResult == 2) {
                playerComputer = "PAPER";
            }
            else if (computerResult == 3) {
                playerComputer = "SCISSORS";
            }

            switch (playerHuman) {
                case "ROCK" :
                    if(playerComputer.equals(playerHuman)) {
                    System.out.println("Tie you both picked \"ROCK\"");
                    numberOfTies++;
                }
                    else if(playerComputer.equals("PAPER")) {
                        System.out.println("Computer wins!");
                        playerComputerWins++;
                    }
                    else {
                        System.out.println("You win, \"ROCK\" beats " + "\"" + playerComputer + "\"");
                        playerHumanWins++;
                        return;
                    }
                    break;
                case "PAPER" :
                    if(playerComputer.equals(playerHuman)) {
                    System.out.println("Tie you both picked \"PAPER\"");
                    numberOfTies++;
                }
                    else if(playerComputer.equals("ROCK")) {
                        System.out.println("You win, \"PAPER\" beats " + "\"" + playerComputer + "\"");
                        playerHumanWins++;
                        return;
                    }
                    else {
                        System.out.println("Sorry, the computer won!");
                        playerComputerWins++;
                    }
                    break;
                case "SCISSORS" :
                    if(playerComputer.equals(playerHuman)) {
                    System.out.println("Tie you both picked \"SCISSORS\"");
                    numberOfTies++;
                }
                    else if(playerComputer.equals("PAPER")) {
                        System.out.println("You win, \"SCISSORS\" beats " + "\"" + playerComputer + "\"");
                        playerHumanWins++;
                        return;
                    }
                    else {
                        System.out.println("Sorry, the computer won!");
                        playerComputerWins++;
                    }
                    break;
                default:
                    playerHuman = playerHuman.toLowerCase();
                    System.out.println("Sorry, " + playerHuman + " is not a valid entry..."); 
                    break;
            } 
        }
    }         
}
}

The problem that I'm facing is related to the winning calculations. When I run the program and I enter rock repeatedly until I win, the output will be You win, "ROCK" beats " " but with any other option I get You win, "ROCK" beats "PAPER"

My question is, why am I getting an empty callback when playing rock?

* Also if you'd be willing to point out any other suggestions to help out a novice that would be great. *

Answer 1

Math.random() * 3 is a number at least 0 and less than 3.

After casting it to an int, it is 0, 1, or 2.

        if(computerResult == 0) {
            playerComputer = "ROCK";
        }
        else if(computerResult == 1) {
            playerComputer = "PAPER";
        }
        else if (computerResult == 2) {
            playerComputer = "SCISSORS";
        }

Suggestions:

Be concise. You could change

String startGame;
startGame = input.nextLine();
startGame = startGame.toUpperCase();

to

String startGame = input.nextLine().toUpperCase();

It's more readable when you don't have to scroll and scroll.

Also, know that equalsIgnoreCase() exists.

Answer 2

This is not for a complete novice, but I would model the game using this code:

enum Choice { ROCK, PAPER, SCISSORS }

enum Result { COMPUTER_WINS, TIE, HUMAN_WINS }

Result decide(Choice computer, Choice human) {
  if (human == computer) {
    return Result.TIE;
  } else if (…) {
    …
  }
}

That way you have some part of the code that handles the game itself, while some other code handles the user interaction.

Answer 3

You will find that (int)(Math.random() * 3) results in 0 sometimes and never 3, which is what is giving you your blank, as you don't have a result for 0.

Specifically, its when Math.random() returns less than .33