Java Do While 无法正常工作

Question

抱歉，我是这个网站的新手，所以不确定它会如何显示。我正在尝试制作一个简单的石头剪刀布游戏。在 while 语句之后，如果没有输入 R、P、S，则程序不执行任何操作。我希望它循环回到开头的问题，以便可以输入正确的选择。另外，我如何输入“无效选择，请重试”之类的打印语句？

package rps.gameapp;

import java.util.Scanner;

public class RPSGameApp
{

    public static void main(String[] args)
    {

    Scanner sc = new Scanner(System.in);
    String userChoice;
    String playAgain;
    int randNum = (int) (Math.random() * 3);

    do
        {
        System.out.println("Welcome to Rock, Paper, Scissors Game.");
        System.out.println("Pick R, P, or S.");
        userChoice = sc.nextLine();
        while (!userChoice.equalsIgnoreCase("P")
                && !userChoice.equalsIgnoreCase("R")
                && !userChoice.equalsIgnoreCase("S"));


            String compChoice = "";
        switch (randNum)
            {
            case 0:
                compChoice = "R";
                break;
            case 1:
                compChoice = "P";
                break;
            case 2:
                compChoice = "S";
                break;
            }

        System.out.println("The computer entered \"" + compChoice + "\".");

        if (compChoice.equalsIgnoreCase(userChoice))
            {
            System.out.println("Draw");
            } else if (userChoice.equalsIgnoreCase(userChoice)
                && compChoice.equalsIgnoreCase("S")
                || userChoice.equalsIgnoreCase("P")
                && compChoice.equalsIgnoreCase("R")
                || userChoice.equalsIgnoreCase("S")
                && compChoice.equalsIgnoreCase("P"))
            {
            System.out.println("User Wins");
            } else
            {
            System.out.println("User Loses");
            }

        System.out.print(
                "Do you want to play again? (Y/N)");
        playAgain = sc.nextLine();

        } while (playAgain.equalsIgnoreCase("Y"));

    System.out.println("Thanks for Playing!");

    }
}

Answer 1

看起来您忘记了内部 do while 循环的一个 do。

应该是:

do {
    do {
        System.out.println("Welcome to Rock, Paper, Scissors Game.");
        System.out.println("Pick R, P, or S.");
        userChoice = sc.nextLine();
    } while (!userChoice.equalsIgnoreCase("P") && !userChoice.equalsIgnoreCase("R") && !userChoice.equalsIgnoreCase("S")); 
    ...
} while (playAgain.equalsIgnoreCase("Y"));

如果没有内部 do (以及围绕该循环主体的花括号)，内部循环将成为一个具有空主体的 while 循环。