java如何处理无效的用户输入？

Question

对于我的餐厅选择器程序，我需要编写一个使用决策结构的程序：在编译和运行它时，我会遇到一些错误，例如：

Exception in thread "main" java.util.InputMismatchException
  at java.base/java.util.Scanner.throwFor(Scanner.java:939)
  at java.base/java.util.Scanner.next(Scanner.java:1594)
  at java.base/java.util.Scanner.nextBoolean(Scanner.java:1893)
  at ABaybayanAssignment3.main(ABaybayanAssignment3.java:12)

我想知道我能对我的代码做些什么来修复它。我的代码可以在下面找到

import java.util.Scanner;

public class ABaybayanAssignment3 {
    public static void main(String[]args) {
        
    Scanner scnr = new Scanner(System.in);
        
    
        System.out.println("Type yes or no for the following questions:");
        
        System.out.println("Is anyone in your party vegetarian?");
        boolean Vegetarian = scnr.nextBoolean();
        
        System.out.println("Is anyone in your party vegan?");
        boolean vegan = scnr.nextBoolean();
        
        System.out.println("Is anyone in your party gluten free?");
        boolean glutenFree = scnr.nextBoolean();
        
        System.out.println("Here are your restaurant choices:");
        
        if(Vegetarian || vegan || glutenFree ) {
            System.out.println("Corner Cafe");
        }
        if(!Vegetarian && !vegan && !glutenFree) {
            System.out.println("Joe's Gourmet Burgers");
        }
        if(!vegan) {
            System.out.println("Main Street Pizza Company");
        }
        if(!vegan && !glutenFree) {
            System.out.println("Mama's Fine Italian");
        }
    }
}

Answer 1

我认为主要的问题是你不能处理无效的输入错误。最好捕获这些异常，并提示用户输入有效的输入。或者，您还可以添加一个默认值，在用户未输入任何内容的情况下，将布尔值设置为该值（当然，在程序开始时指定）

这样的事情应该有助于传达我的意思：

public class ABaybayanAssignment3 {

    public static void main(String[] args) {

        Scanner scnr = new Scanner(System.in);

        System.out.println("Type yes or no for the following questions:");

        boolean Vegetarian = requestBooleanInput(scnr,"Is anyone in your party vegetarian?" );
        boolean vegan = requestBooleanInput(scnr,"Is anyone in your party vegan?");
        boolean glutenFree = requestBooleanInput(scnr,"Is anyone in your party gluten free?");

        System.out.println("Here are your restaurant choices:");

        if (Vegetarian || vegan || glutenFree) {
            System.out.println("Corner Cafe");
        }
        if (!Vegetarian && !vegan && !glutenFree) {
            System.out.println("Joe's Gourmet Burgers");
        }
        if (!vegan) {
            System.out.println("Main Street Pizza Company");
        }
        if (!vegan && !glutenFree) {
            System.out.println("Mama's Fine Italian");
        }
    }

    public static boolean requestBooleanInput(Scanner scanner, String message){
        boolean value = false;
        boolean validInput = false;
        while (!validInput){
            System.out.println(message);
            try {
                value = scanner.nextBoolean();
                validInput = true;
            } catch (Exception e) {
                System.out.println("You entered an invalid input '"+scanner.next()+"', please enter only 'true' or 'false'");
            }
        }
        return value;
    }
}

Answer 2

程序编译和运行时没有任何错误

程序的问题是在运行时将yes和no赋值给布尔变量Vegetarian，vegan，glutenFree，这是错误的

<强>也不同于C++，java中的布尔值不能赋给< < />强> ->仅<强>真< <强> >或<强> false <强> >。p>

此外，改变

System.out.println("Type yes or no for the following questions:");

到

System.out.println("Type true or false for the following questions:");

Answer 3

我有一个解决方案。我使用了Boolean并使用了true/false而不是yes/no。两者在逻辑上是相同的。这是我的节目

public class testing {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);


        System.out.println("Type true or false for the following questions:");

        System.out.println("Is anyone in your party vegetarian?\n");
        boolean Vegetarian = sc.nextBoolean();

        System.out.println("Is anyone in your party vegan?\n");
        boolean vegan = sc.nextBoolean();

        System.out.println("Is anyone in your party gluten free?\n");
        boolean glutenFree = sc.nextBoolean();

        System.out.println("Here are your restaurant choices:");

        if(Vegetarian == true && vegan == true && glutenFree == true) {
            System.out.println("Corner Cafe");
        } else if(Vegetarian == false && vegan == false && glutenFree == false) {
            System.out.println("Joe's Gourmet Burgers");
        } else if(vegan == false) {
            System.out.println("Main Street Pizza Company");
        } else if(vegan == false && glutenFree == false) {
            System.out.println("Mama's Fine Italian");
        }

    }

}

我的结果显示

Type true or false for the following questions:
Is anyone in your party vegetarian?

true
Is anyone in your party vegan?

true
Is anyone in your party gluten free?

true
Here are your restaurant choices:
Corner Cafe

我已经改变了程序，当然是为了让它更容易。由于使用了Boolean，那么唯一的选项是true或false。除此之外，if-else验证也被修改为abit，以补充true/false输入。所以我希望这能回答你的问题