关于扫描仪（BlueJ）的问题

Question

我们对此任务有一些指导方针：1。使用scanner（scanner scanner=new scanner（system.in）；）2。使用方法scanner.nextline（）

我们必须一步一步地构建一个游戏(Mastermind)，我总是在使用nextInt（）和switchcase（用于输入不是int的东西）时出错（BlueJ）顺便说一句：我们不应该使用nextint-我们应该使用nextline--但我如何使用switchcase来实现这一点？

import java.util.Scanner;
public class Game {
/**
 * Methods
 */
public void play() {
    System.out.println("*******************  Game  **********************");
    System.out.println("* (1) CPU vs Human                              *");
    System.out.println("* (2) CPU vs CPU                                *");
    System.out.println("* (3) Human vs CPU                              *");
    System.out.println("* (4) Highscore                                 *");
    System.out.println("* (5) End                                       *");
    System.out.println("-------------------------------------------------");
    System.out.println("Your choice:                                    ");

    Scanner scanner = new Scanner(System.in);

    // i used this so far but i get an error for entering a-z or other stuff than numbers
    int userInput = scanner.nextInt();  

    //i have to use this but it doesnt work with switchcase - any suggestions?
    //String userInput = scanner.nextLine(); 

    scanner.close();
    switch(userInput) {
        case 1: // not written yet
        case 2: // not written yet
        case 3: // not written yet
        case 4: // not written yet
        case 5: System.exit(0);
        default: System.out.println("Illegal userinput! Only enter numbers between 1 and 5!");
    }
  }
}

Answer 1

您需要做的是使用integer.parseInt(strings)方法将字符串（由.nextline()方法生成）解析为整数。如果给定的字符串不是整数，此方法将抛出NumberFormatException，您可以捕获该字符串并使用它来了解用户何时输入了无效的数字，以便再次询问他/她。

类似于：

public static void main(String[] args)
{
    boolean validInput = false;
    Scanner scanner = new Scanner(System.in);
    while (!validInput)
    {
        System.out.println("*******************  Game  **********************");
        System.out.println("* (1) CPU vs Human                              *");
        System.out.println("* (2) CPU vs CPU                                *");
        System.out.println("* (3) Human vs CPU                              *");
        System.out.println("* (4) Highscore                                 *");
        System.out.println("* (5) End                                       *");
        System.out.println("-------------------------------------------------");
        System.out.println("Your choice:                                    ");

        try
        {

            // i used this so far but i get an error for entering a-z or other stuff than numbers
            int userInput = Integer.parseInt(scanner.nextLine().trim());
            //If no error took place, then the input is valid.
            validInput = true;

            //i have to use this but it doesnt work with switchcase - any suggestions?
            //String userInput = scanner.nextLine();                 
            switch (userInput)
            {
                case 1: // not written yet
                case 2: // not written yet
                case 3: // not written yet
                case 4: // not written yet
                case 5:
                    System.exit(0);
                default:
                    validInput = false;
                    System.out.println("Illegal userinput! Only enter numbers between 1 and 5!");
            }
        } catch (Exception e)
        {
            System.out.println("Invalid Input, please try again");
        }
    }
    scanner.close();
}