我的扫描器类java代码有一个异常，这是一个错误

Question

我在运行代码时遇到此错误，请帮助

Exception in thread "main" java.util.InputMismatchException

如果您能对代码进行全面的修复，我将不胜感激

在这种情况下，当我输入像重量这样的数据时，它充满了错误，而且很烦人

package howto;

import java.util.Scanner;


public class Howto {


    public static void main(String[] args) {
        Scanner sc1 = new Scanner(System.in);

        Scanner sc2 = new Scanner(System.in);

        double weightkg [] = new double [30];

        double weightkgEndOfMonth [] = new double [30];

        String name [] = new String [30];

        double weightDifference [] = new double[30];



        for (int i = 0; i<31; i++)

        {

            System.out.println("Input name: ");

            String scanner1 = sc1.nextLine();



            name [i] = scanner1;



            System.out.println("Input weight: ");

            double scanner2 = sc2.nextDouble();



            if(!sc1.hasNextDouble())

            {

                System.out.println("Invalid Weight!. Start Again");

            } else

            {

                weightkg[i] =  scanner2;

            }



            System.out.println("Name: " + name[i]);

            System.out.println("weight : " + weightkg[i]);



        }



        for (int i = 0; i<31; i++)

        {



            System.out.println("Input weight at the end of month: ");

            double scanner2 = sc2.nextDouble();



            if(!sc1.hasNextDouble())

            {

                System.out.println("Invalid Weight!. Start Again");

            } else

            {

                weightkgEndOfMonth[i] =  scanner2;

            }



            weightDifference [i] = weightkg[i] - weightkgEndOfMonth[i];



            if(weightDifference[i]>2.5)

            {

                System.out.println("Student with a weight difference greater than 2.5kg: " + name[i]);

                System.out.println("Weight difference: " + weightDifference[i]);

                System.out.println("Rise");

            }



            if(weightDifference[i]> -2.5)

            {

                System.out.println("Student with a weight difference greater than 2.5kg: " + name[i]);

                System.out.println("Weight difference: " + weightDifference[i]);

                System.out.println("Fall");

            }

        }

    }

}

错误消息：

run:
Input name: 
Test
Input weight: 
90
10
Name: Test
weight : 90.0
Input name: 
Input weight: 
Test1
Exception in thread "main" java.util.InputMismatchException
    at java.util.Scanner.throwFor(Scanner.java:864)
    at java.util.Scanner.next(Scanner.java:1485)
    at java.util.Scanner.nextDouble(Scanner.java:2413)
    at howto.Howto.main(Howto.java:45)
Java Result: 1
BUILD SUCCESSFUL (total time: 16 seconds)

Answer 1

你的代码中有一些逻辑错误。每一行我都提到他们

import java.util.Scanner;

public class HowTo {

  public static void main(String[] args) {
    Scanner sc1 = new Scanner(System.in); // you need only 1 scanner
    double weightkg[] = new double[30];
    double weightkgEndOfMonth[] = new double[30];
    String name[] = new String[30];
    double weightDifference[] = new double[30];
    for (int i = 0; i < 30; i++) { // need to iterate from 0 index to 29
      System.out.print("Input name: ");
      String scanner1 = sc1.nextLine();
      name[i] = scanner1;
      System.out.print("Input weight: ");
      if (!sc1.hasNextDouble()) {
        System.out.println("Invalid Weight!. Start Again");
      } else {
        weightkg[i] = sc1.nextDouble();// if it has double then read it 
      }
      System.out.println("Name: " + name[i]);
      System.out.println("weight : " + weightkg[i]);
      sc1.nextLine();
    }
    for (int i = 0; i < 30; i++) {// need to iterate from 0 index to 29
      System.out.println("Input weight at the end of month: ");
      if (!sc1.hasNextDouble()) {
        System.out.println("Invalid Weight!. Start Again");
      } else {
        weightkgEndOfMonth[i] = sc1.nextDouble();// read double here 
      }
      weightDifference[i] =weightkgEndOfMonth[i]- weightkg[i] ;// weight difference is (final weight- initial weight)
      if (weightDifference[i] > 2.5) {
        System.out.println("Student with a weight difference greater than 2.5kg: " + name[i]);
        System.out.println("Weight difference: " + weightDifference[i]);
        System.out.println("Rise");
      }
      if (weightDifference[i] < -2.5) {// fall if weight less than 2.5
        System.out.println("Student with a weight difference greater than 2.5kg: " + name[i]);
        System.out.println("Weight difference: " + weightDifference[i]);
        System.out.println("Fall");
      }

    }

  }
}

现在它运行良好

Answer 2

有几个问题很突出

首先

Scanner sc1 = new Scanner(System.in);
Scanner sc2 = new Scanner(System.in);

你不需要多个扫描仪，反正它们都是从同一个流中读取的，最好只使用一个，减少复杂性

接下来

String scanner1 = sc1.nextLine();
name [i] = scanner1;

System.out.println("Input weight: ");

double scanner2 = sc2.nextDouble();
if(!sc1.hasNextDouble())
{
    System.out.println("Invalid Weight!. Start Again");

} else
{
    weightkg[i] =  scanner2;
}

当使用nextDouble时，缓冲区仍然包含一个换行标记，这意味着下次使用nextLine时，它将返回一个空白String并继续

另外，hasNextDouble似乎在等待数据，但您已经从缓冲区读取了double值，留下了悬而未决的新行。在我的测试中，这导致程序在等待更多输入时出现问题

我通过这样做“解决”了基本问题

String scanner1 = sc1.nextLine();
name [i] = scanner1;

System.out.println("Input weight: ");

double scanner2 = sc1.nextDouble();
weightkg[i] =  scanner2;
sc1.nextLine();

现在这个“会”起作用，但它不是最好的解决方案。另一种“不同”的方法可能是将权重读入为String，并尝试将其解析为double，这使您有机会捕获无效输入，并以更合适的方式处理它，例如

System.out.println("Input name: ");

String scanner1 = sc1.nextLine();

name[i] = scanner1;

boolean done = false;
double weight = 0;
do {
    System.out.println("Input weight: ");
    String input = sc1.nextLine();
    try {
        weight = Double.parseDouble(input);
        done = true;
    } catch (NumberFormatException nfe) {
        System.out.println("!! Invalid value");
    }
} while (!done);
weightkg[i] = weight;

System.out.println("Name: " + name[i]);

System.out.println("weight : " + weightkg[i]);

}