Question

我一直在努力学习扫描仪课程。我似乎无法用它来解释它的方法。我正在尝试运行一组似乎对我来说正确的代码。我尝试了一些调整但仍然没有。我收到此错误的任何提示

“线程中的异常”主“java.util.InputMismatchException at java.util.Scanner.throwFor（未知来源）at java.util.Scanner.next（未知来源）at java.util.Scanner.nextInt（未知来源）at java.util.Scanner.nextInt（未知来源）at PolynomialTest.main（PolynomialTest.java:18）“

public class PolynomialTest {

public static void main(String[] args) throws IOException {

Scanner fileData = new Scanner(new File("operations.txt"));
Polynomial math = new Polynomial();
int coeff = fileData.nextInt();
int expo = fileData.nextInt();

while (fileData.hasNext()) {

    Scanner nextTerm = new Scanner(fileData.nextLine());

    if (nextTerm.next().equalsIgnoreCase("insert")) {

        math.insert(coeff, expo);
        System.out.println("The term (" + coeff + ", " + expo
                + ") has been added to the list in its proper place");
        System.out.println("The list is now: " + math.toString());

    } else if (nextTerm.next().equalsIgnoreCase("delete")) {

        math.delete(coeff, expo);
        System.out.println("The following term has been removed ("
                + coeff + ", " + expo + ")");
        System.out.println("The list is now: " + math.toString());

    } else if (nextTerm.next().equalsIgnoreCase("reverse")) {

        math.reverse();
        System.out
                .println("The list was reversed in order and the list is now: "
                        + math.toString());

    } else if (nextTerm.next().equalsIgnoreCase("product")) {

        System.out.println("The product of the polynomial is: "
                + math.product());

    } else {

        System.out.println("Not a recognized input method");

    }
    nextTerm.close();
}
PrintWriter save = new PrintWriter("operations.txt");
save.close();
fileData.close();

}

Answer 1

您的代码存在许多问题。在nextLine()之后从未致电while(hasNext())。您的while循环应为

while (fileData.hasNextLine()) {
   Scanner nextTerm = new Scanner(fileData.nextLine());

您在每个nextTerm.next()声明中致电if-else。您应该分配一个名为operation的String变量。

   String operation=nextTerm.next();

   if (operation.equalsIgnoreCase("insert")) {
      ....
   } else if (operation.equalsIgnoreCase("delete")) {
    ..........
   } 
   ...
   else if (operation.equalsIgnoreCase("product")) {
     .....
   }

Answer 2

扫描程序抛出InputMismatchException以指示检索到的标记与预期类型的模式不匹配，或者标记超出预期类型的范围。

int coeff = fileData.nextInt();
int expo = fileData.nextInt();

尝试将上面的内容更改为如下所示。（如果您在2个单独的行中有前2个整数输入，否则在使用fileData.nextLine().split(" ")读取它们之后尝试解析它们）

int coeff  = Integer.parseInt(fileData.nextLine());
int expo = Integer.parseInt(fileData.nextLine());

如果同一行中有2个整数

    String s[] = fileData.nextLine().split(" ");
    int coeff   = Integer.parseInt(s[0]);
    int expo  = Integer.parseInt(s[1]);

如果您也可以发布Polynomial课程，那就太好了。

Scanner类和线程“main”java.util.InputMismatchException错误中的异常

2 个答案: