異常處理在運行程序中只能運行一次

Question

最初我試圖將try語句放入while循環中，但是，遇到了幾個錯誤。 該程序運行完美，除非我輸入一個不規則字符，一旦它給我輸入我創建的打印行，但是，當我再次輸入另一個時，該行不會彈出，而是給我一個格式異常錯誤。

AddNumbersrealone2.java

import java.io.*;

// create the class
public class AddNumbersrealone2
{
    // allows i/o
  public static void main (String [] args) throws IOException
  {   // initalize variables and strings
    BufferedReader myInput = new BufferedReader  (new InputStreamReader (System.in));
    String sumNumbers;
    //String go;
    double num ;
    double total = 0.0;

    // asks user questions and instructions
    System.out.println("Hello, the following program will ask for your input of a number ");
    System.out.println("Each time you input a number a running total will be added to each previous number")  ;
    System.out.println("Once ready input a number to start!");
    // try and catch block      
    try {

      num = 0;

      // while statement if this occurs stop the program, in this case if a negative integer is inputted

      while (num >= 0) {

        // Contious question asked  
        System.out.println("Input another number..."); 
        sumNumbers = myInput.readLine();
        num = Double.parseDouble (sumNumbers);

        // calculates number (Running total)
        total = total + num;
        System.out.println(total);

        // end error trap
      }
    }
    catch  (Exception e){
      System.out.println("Please refrain from entering regular characters!");
      num = 0;

      // re- while statement if this occurs stop the program, in this case if a negative integer is inputted

      while ( num >= 0) {

        // input question after a character is inputted
        System.out.println("Please input a number: ");
        sumNumbers = myInput.readLine();
        num = Double.parseDouble (sumNumbers);

        total = total + num;
        System.out.println(total);

        // ending statement
      }
    }
    System.out.println("You entered a negative number, the program will exit now");
    System.out.println("Good-bye!");

    // Complete class body
  }
}

Answer 1

你想要一些東西來捕捉Double.parseDouble周圍的異常

例如。

 while(num >= 0)
    {
    // input question after a character is inputted
       System.out.println("Please input a number: ");
       sumNumbers = myInput.readLine();
       try{
            num = Double.parseDouble (sumNumbers);
            total = total + num;
            System.out.println(total);
       } catch(Exception e)
       {
            System.out.println("Please enter a proper number");
       }    


            // ending statement
  }

Answer 2

您的問題是，只要拋出第一個異常，您的程序就會陷入catch語句內的while（）循環中。 因此，如果輸入了另一個無效輸入，則在第二個while循環中處理它，其中沒有try-catch語句。 一個很好的解決方法是讓你的try語句只包含你所說的num = Double.parseDouble（sumNumbers）;的行。 捕獲異常時，以continue結束; 聲明，以便您的程序循環回頭，並要求另一個輸入。