我的扫描仪类 java 代码有一个异常是错误

Question

运行我的代码时出现此错误，请帮助。线程“main”中的异常 java.util.InputMismatchException我将不胜感激您可以为整个代码提供的任何修复。在这种情况下，当我输入重量等数据时，它充满了错误并且很烦人。错误信息：run:Input name: TestInput weight: 9010Name: Testweight : 90.0Input name: Input weight: Test1Exception 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: 1BUILD SUCCESSFUL (total time: 16 seconds)

Answer 1

有几个问题很突出……

第一的...

Scanner sc1 = new Scanner(System.in);

Scanner sc2 = new Scanner(System.in);

您不需要多个扫描仪，无论如何它们都从同一个流中读取，最好只使用一个并降低复杂性。

下一个...

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;

}

使用时nextDouble，缓冲区仍包含换行符，这意味着下次使用时nextLine，它将返回空白String并继续。

此外，hasNextDouble似乎在等待数据，但您已经double从缓冲区中读取了值，留下了悬空的新行。在我的测试中，这导致程序等待更多输入出现问题。

我通过做这样的事情“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“将”起作用，但这不是最好的解决方案。“不同”的方法可能是将权重作为 a 读取String并尝试将其解析为 a 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]);

}

Answer 2

你的代码中有一些逻辑错误。在每一行之后我都会提到它们。

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");

      }

    }

  }

}

现在它工作正常。