如何使異常處理循環（無限次數）

Question

對此處鏈接的前一個問題（https://stackoverflow.com/questions/15487706/try-and-catch-block-not-functioning-in-user-defined-method）的迴應，我對該問題的初步解答已得到解決，但是當它涉及到後來解決的循環時，我遇到了另一個問題通過簡單地使用for循環。但是，我的問題是我不希望用戶在處理異常之後不得不重新啓動程序，而是希望它將相同的開始問題循環到用戶。我試着在返回語句之後放置打印語句，並嘗試在try catch之後完全複製邏輯代碼，但是，意識到這不會導致用戶爲異常循環無限次。另外，在附註中，是的，我之前的問題有很好的答案，然而，沒有人設法回答我更多反覆出現的問題，這就是爲什麼沒有人得到答覆的答案。

import java.io.*; 
import java.text.DecimalFormat; 

public class Test 
{ 

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

     double x; 
     x = circlemethods(0.0, 0.0, 0.0, 1.0); 

    } 

    public static double circlemethods(double volume, double surfacearea, 
      double area, double radius) throws IOException 
    { 

     BufferedReader myInput = new BufferedReader(new InputStreamReader(System.in)); 

     String numInput; 
     String reqInput; 
     String amountStr; 
     double numInt = 0; 
     double num = 0; 
     double answer = 0; 
     double amount = 0; 
     double answer2 = 0; 
     double answer3 = 0; 
     double answer4 = 0; 

     for (double i = 0; i < 999; i++) 
      ; 
     try 
     { 

      // for (double i = 0; i < 999; i++); 

      // while (numInt != 999) { 

      System.out.println("This program will ask for a given user radius, then proceed to calculate the user input"); 
      System.out.println("The program will use four methods to achieve this, all calling back to the main method"); 
      System.out.println("Press any key to continue"); 
      numInput = myInput.readLine(); 

      System.out.println("First, what would you like to calculate?"); 
      System.out.println("Enter '1' for Circumference, '2' for area, '3' for volume, or '4' for surface area"); 
      reqInput = myInput.readLine(); 
      numInt = Double.parseDouble(reqInput); 

      System.out.println("Now enter the radius of the required shape(Half of diameter)"); 
      numInput = myInput.readLine(); 
      num = Double.parseDouble(numInput); 

      DecimalFormat nextAmount = new DecimalFormat("0.00"); 
      amountStr = nextAmount.format(amount); 

      if (numInt == 1) 
      { 
       System.out.println("You chose to calculate circumference, given the radius :" + num); 
       answer = (3.14) * (2) * (num); 
       System.out.print("The circumference of that sphere is :"); 
       System.out.println(answer + "cm³"); 
       return answer; 
      } 
      else if (numInt == 2) 
      { 
       System.out.println("You chose to calculate area, given the radius :" + num); 
       answer2 = (3.14) * 2; 
       System.out.print("The area of the circle is :"); 
       System.out.println(answer2 + "cm²"); 
       return answer2; 
      } 
      else if (numInt == 3) 
      { 
       System.out.println("You chose to calculate volume, given the radius :" + num); 
       answer3 = 4/3 * (3.14) * (num) * (3) * (3) * (3); 
       System.out.print("The volume of that sphere is : cm³"); 
       System.out.println(answer3 + "cm³"); 
       return answer3; 
      } 
      else 
      // if (numInt == 4) 
      { 
       System.out.println("You chose to calculate surface area, given the radius :" + num); 
       answer4 = 4 * (3.14) * (num) * (2) * (2); 
       System.out.print("The Surface area of that sphere is :"); 
       System.out.println(answer4 + "cm²"); 
       return answer4; 

      } 

     } catch (Exception e) 
     { 
      System.out.println("Please do not enter any string values, next time input enter a number "); 
      return 0; 
      // how to loop this untill the user inputs a number???? 

     } 

    } 

} 

Answer 1

首先，您使用while(true)循環，而不是循環999次。 （考慮到它後面有分號，該循環實際上沒有做任何事情。）

然後，您從catch塊中刪除return 0;塊。

因此，這將是

while(true) { 
    try { 
     .... //your code 
    } 
catch {...} 
} //while loop end bracket 

這樣，如果它達到你return語句的一個循環纔會結束。

Answer 2

您需要循環，直到獲得有效值。一種方法是循環直到布爾值被設置爲true。嘗試與此類似：

boolean inputIsValid = false; 
while (!inputIsValid) { ... 

然後當你已經確定你有一個有效的輸入，添加一行：

inputIsValid = true; 

你的循環將繼續下去，直到inputIsValid爲真。

你也可以創建一個無盡的while循環。然後，當你收到有效輸入，break圈外：

while(true) { 
    //when valid input is received 
    break; 
}