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java - 在打印错误消息后，我如何将用户困在一个循环中，直到给出有效输入？

问题描述

我想询问用户输入，如果它无效，我将推出一个错误语句并要求用户输入另一个输入。我将如何编写一个循环来让用户在收到错误后保持相同的输入请求？我以前使用的方法是 Python 中的 try 和 except。Java中的等价物是什么？

import java.util.Scanner;
import java.util.Random;
public class Main {
  //Setting Moves List
  enum Move {
    ROCK,
    PAPER,
    SCISSORS
  }
  //Initiate Scanner and accept user input
  public static String getUserMove() {
    Scanner keyboard = new Scanner(System.in);
    String gesture = keyboard.nextLine();
    String userMove = gesture.toUpperCase();
    if (userMove.equals("ROCK") || userMove.equals("PAPER") || userMove.equals("SCISSORS")) {
      return userMove;
    } else {
      System.out.println("This is not a valid input." +
        "Please try again!");
      return "Invalid Input";
    }
  }
  //Get random input as CPU move
  public static String getAiMove() {
    String Ai;
    Random random = new Random();
    int input = random.nextInt(3);
    if (input == 1) {
      Ai = Move.ROCK.name();
    } else if (input == 2) {
      Ai = Move.PAPER.name();
    } else {
      Ai = Move.SCISSORS.name();
    }
    return Ai;
  }
  //Determine Winner Result
  public static void main(String args[]) {
    System.out.println("Choose your move against the CPU:");
    System.out.println("ROCK, PAPER, OR  SCISSORS");

    String playerMove = getUserMove();
    System.out.println("You threw: " + playerMove);
    if (!playerMove.equals("Invalid Input")) {
      String cpuMove = getAiMove();
      System.out.println("Computer threw: " + cpuMove);
      if (playerMove.equals(cpuMove)) {
        System.out.println("Tie! Nobody Wins!");
      }
      // Player is Rock
      else if (playerMove.equals(Move.ROCK.name())) {
        if (cpuMove.equals(Move.PAPER.name())) {

          System.out.println("You Lost! \nPaper beats Rock!");
        } else {
          System.out.println("You Win! \nRock beats Scissors!");
        }
      }
      // Player is Paper
      else if (playerMove.equals(Move.PAPER.name())) {
        if (cpuMove.equals(Move.SCISSORS.name())) {
          System.out.println("You Lost! \nScissors beats Paper!");
        } else {
          System.out.println("You Win! \nPaper beats Rock!");
        }
      }
      // Player is Scissors
      else {
        if (cpuMove.equals(Move.ROCK.name())) {
          System.out.println("You Lost! \nPaper beats Rock!");
        } else {
          System.out.println("You Win! \nRock beats Scissors !");
        }
      }
    }
  }
}

标签： javaloops

解决方案

除了你的 if 语句getUserMove()，你可以尝试这样的事情，这将强制用户输入一个有效的gesture.

  //Initiate Scanner and accept user input
  public static String getUserMove() {
    Scanner keyboard = new Scanner(System.in);
    String gesture = keyboard.nextLine().toUpperCase();

    while(!(userMove.equals("ROCK") || userMove.equals("PAPER") || userMove.equals("SCISSORS"))){
       System.out.println("This is not a valid input." + "Please try again!");
       gesture = keyboard.nextLine().toUpperCase();
    }
    return gesture;
  }

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