如何在我的程序中使用 try/catch/finally 过滤扫描仪输入错误？

Question

我写了这个小猜谜游戏，你必须猜出一个随机数。 我完成了这个程序，但我想做的最后一件事是：当用户应该输入一个数字及其和 InputMissmatching 错误或其他错误时，系统告诉他必须输入一个大于 0 的数字。但是变量在此 do-while 循环之后，扫描仪的 不再工作！ 我必须如何使用循环设置 try/catch/finally 以仅获取整数而不是在它不是整数或 0 时崩溃？

问题是guessNumber 和numberOfUser 变量现在还没有被初始化！ 行：37,53 那么我必须在 try/catch 循环中更改什么？

package gessinggame;

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

public class GessingGame {

    public static void main(String[] args) {




//<editor-fold desc="Start Variables and Objects">

        Random random = new Random();
        Scanner input = new Scanner(System.in);

        int counter = 0;
        int numberOfUser;
        int guessNumber;
        int x = 1;
        System.out.print("Try to guess my number! What should be the highest number I can go up to?: ");
        do{
        try{
            numberOfUser = input.nextInt();
            guessNumber = random.nextInt(numberOfUser);
            x = 2;
        }catch(Exception e)
        {
            System.out.print("That doesn't work! Please enter an integer higher than 0 :");
            x = 1;
        }
        }while(x == 1);
//</editor-fold>

//<editor-fold desc="do-while loop (higher/lower/equal)">

        System.out.println("Try to guess my number! Its from 0 to " + numberOfUser + " !");
        System.out.println("---------------------------------------------------");

        do{

                int userguess = input.nextInt();

                    if(userguess > numberOfUser)
                    {
                    System.out.println("Oh man, at the beginning you said that the highest number is: " + numberOfUser);
                    }
                    else{       
                            if(userguess < 0)
                            {
                            System.out.println("My number is always taller than 0");
                            } else{  
                                    if(guessNumber < userguess)
                                    {
                                        System.out.println("lower");
                                        counter++;
                                    }
                                    if(guessNumber > userguess) 
                                    {
                                        System.out.println("higher");
                                        counter++;
                                    }
                                    if(userguess == guessNumber) 
                                    {
                                        counter++;
                                        break;
                                    }
                                    }
                        }
            }while(true);

//</editor-fold>

//<editor-fold desc="print final result">

        System.out.println("You guessed my number! My number was: " + guessNumber + "! You needed " + counter + " attempts!");

//</editor-fold>
    }

}

Answer 1

所以问题是首先你当然需要捕获异常。 在 try catch 中，您必须清除缓冲区，然后使用 input.nextLine();

所以这应该有效：

public static void main(String[] args)
{

    // <editor-fold desc="Start Variables and Objects">

    Random random = new Random();
    Scanner input = new Scanner(System.in);

    int counter = 0;
    int numberOfUser = 0;
    int guessNumber = 0;
    int x = 1;
    System.out.print("Try to guess my number! What should be the highest number I can go up to?: ");
    do
    {
        try
        {
            numberOfUser = input.nextInt();
            guessNumber = random.nextInt(numberOfUser);
            x = 2;
        }
        catch (Exception e)
        {
            System.out.print("That doesn't work! Please enter an integer higher than 0 :");
            x = 1;
        }
    } while (x == 1);
    // </editor-fold>

    // <editor-fold desc="do-while loop (higher/lower/equal)">

    System.out.println("Try to guess my number! Its from 0 to " + numberOfUser + " !");
    System.out.println("---------------------------------------------------");

    do
    {

        int userguess = 0;
        try
        {
            userguess = input.nextInt();
        }
        catch (InputMismatchException e)
        {
            System.out.println("Please enter a valid number!");
            input.nextLine();
        }

        if (userguess > numberOfUser)
        {
            System.out.println("Oh man, at the beginning you said that the highest number is: " + numberOfUser);
        }
        else
        {
            if (userguess < 0)
            {
                System.out.println("My number is always taller than 0");
            }
            else
            {
                if (guessNumber < userguess)
                {
                    System.out.println("lower");
                    counter++;
                }
                if (guessNumber > userguess)
                {
                    System.out.println("higher");
                    counter++;
                }
                if (userguess == guessNumber)
                {
                    counter++;
                    break;
                }
            }
        }
    } while (true);

    // </editor-fold>

    // <editor-fold desc="print final result">

    System.out.println(
            "You guessed my number! My number was: " + guessNumber + "! You needed " + counter + " attempts!");

    // </editor-fold>
}

Answer 2

在try/catch块中添加input.nextLine() 。
在每个Scanner.nextInt之后调用Scanner.nextLine调用以消耗该行的其余部分，包括换行符。

 package gessinggame;

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

public class GessingGame {

    public static void main(String[] args) {




//<editor-fold desc="Start Variables and Objects">

        Random random = new Random();
        Scanner input = new Scanner(System.in);

        int counter = 0;
        int numberOfUser = 0;
        int guessNumber = 0;
        int x = 1;
        System.out.print("Try to guess my number! What should be the highest number I can go up to?: ");
        do{
        try{
            numberOfUser = input.nextInt();
            guessNumber = random.nextInt(numberOfUser);
            x = 2;
        }catch(Exception e)
        {
            System.out.print("That doesn't work! Please enter an integer higher than 0 :");
            input.nextLine();
            x = 1;
        }
        }while(x == 1);


        System.out.println("Try to guess my number! Its from 0 to " + numberOfUser + " !");
        System.out.println("---------------------------------------------------");

        do{

                int userguess = input.nextInt();

                    if(userguess > numberOfUser)
                    {
                    System.out.println("Oh man, at the beginning you said that the highest number is: " + numberOfUser);
                    }
                    else{       
                            if(userguess < 0)
                            {
                            System.out.println("My number is always taller than 0");
                            } else{  
                                    if(guessNumber < userguess)
                                    {
                                        System.out.println("lower");
                                        counter++;
                                    }
                                    if(guessNumber > userguess) 
                                    {
                                        System.out.println("higher");
                                        counter++;
                                    }
                                    if(userguess == guessNumber) 
                                    {
                                        counter++;
                                        break;
                                    }
                                    }
                        }
            }while(true);
        System.out.println("You guessed my number! My number was: " + guessNumber + "! You needed " + counter + " attempts!");
    }

}