如何在Java中获取扫描仪以读取字符串? [英] How do I get the Scanner in java to read a string?

问题描述

当用户输入q时，如何退出程序? 扫描仪有问题吗?

How would I get my program to quit when the user enters q? Is there something wrong with the scanner?

我的代码

import java.util.*;
public class Main{

         public static void main(String []args){
             
             int age;
             
            Scanner scan = new Scanner(System.in);
            System.out.println("Enter your age, or enter 'q' to quit the program.");
            age = scan.nextInt();
            
            
            if(age.equals("q") || age.equals("Q")){
                
                return 0;
                
            }
            
            
            
            System.out.println("Your age is " + age);
            
            
            
         }
    
    }

推荐答案

我在您的代码中主要看到两个问题:

I can see mainly two problems in your code:

1. 它没有循环重复再次要求年龄的问题.有很多方法(for，while，do-while)编写循环，但是我发现

1. It lacks a loop to repeat asking for age again. There can be many ways (for, while, do-while) to write a loop but I find do-while most appropriate for such a case as it always executes the statements within the do block at least once.
2. age is of type, int and therefore it can not be compared with a string e.g. your code, age.equals("q") is not correct. A good way to handle such a situation is to get the input into a variable of type, String and check the value if it should allow/disallow processing it (e.g. trying to parse it into an int).

请注意，当您尝试解析无法解析为int(例如"a")的字符串时，会得到一个需要处理的NumberFormatException(例如，显示错误消息，更改某些状态)等).

Note that when you try to parse a string which can not be parsed into an int (e.g. "a"), you get a NumberFormatException which you need to handle (e.g. show an error message, change some state etc.).

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        int age;
        String input;
        Scanner scan = new Scanner(System.in);
        boolean valid;

        do {
            // Start with the assumption that input will be valid
            valid = true;
            System.out.print("Enter your age, or enter 'q' to quit the program: ");
            input = scan.nextLine();

            if (!(input.equals("q") || input.equals("Q"))) {
                try {
                    // Try to parse input into an int
                    age = Integer.parseInt(input);
                    System.out.println("Your age is " + age);
                } catch (NumberFormatException e) {
                    System.out.println("Invalid input");
                    // Change the value of valid to false
                    valid = false;
                }
            }
        } while (!valid || !(input.equals("q") || input.equals("Q")));
    }
}

示例运行:

Enter your age, or enter 'q' to quit the program: a
Invalid input
Enter your age, or enter 'q' to quit the program: 12.5
Invalid input
Enter your age, or enter 'q' to quit the program: 14
Your age is 14
Enter your age, or enter 'q' to quit the program: 56
Your age is 56
Enter your age, or enter 'q' to quit the program: q

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