尝试循环循环时遇到Java错误

Question

这是我收到的错误消息：

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 calcSums.main(calcSums.java:24)

---

这是我的代码：

import java.util.Scanner;

public class calcSums
{
	public static void main(String[] args)
	{
	    calcSum:{
	        Boolean again = Boolean.valueOf("y");
		    Scanner keyboard = new Scanner (System.in);
		    double number;
		    double sum = 0;
		    System.out.println("Enter a positive number");
		    number = keyboard.nextDouble();
		    while (number > 0)
		    {
			    sum = sum + number;
			    System.out.println("Enter another positive number, enter 0 or negative to end");
			    number = keyboard.nextDouble();
			
		    }
		    System.out.println("The sum is: ");
		    System.out.println(sum);
	        System.out.println("Would you like to find another sum? (y/n)");
	        again = keyboard.nextBoolean();
	        if (again.equals("y"))  {
	        break calcSum; }
	    }
	}
}

由于我不使用.equals，并且在允许我执行我认为已完成的代码时，我之前收到关于如何实现if语句的错误消息，然后当我尝试循环访问再次阻止它给了我错误消息

Answer 1

这是因为您不能输入“ y”作为布尔值。布尔值的字符串表示形式为“ true”或“ false”。
只需像这样在字符串中更改再次变量：

String again = new String();
... //Your other code
System.out.println("Would you like to find another sum? (y/n)");
again = keyboard.nextLine();
if (again.equalsIgnoreCase("y"))  {
    break calcSum; 
}

还要考虑使用另一个while循环而不是您的calcsum-label。

String again = new String("y");
while(again.equalsIgnoreCase("y"){
   ... //Your other code

    System.out.println("Would you like to find another sum? (y/n)");
    //again = keyboard.nextLine();
    again = new Scanner(System.in).nextLine();
}