驗證倍數輸入

Question

我不希望用戶輸入負值。我如何檢測負值和InputMismatchException？這是迄今爲止的代碼！該代碼似乎並不正確，並且無法確定問題出在哪裏。我想驗證用戶輸入以確保負數，字符串和double無效，並提示用戶輸入正確的數字，該數字應該是正整數。

  do { 
       try { 
        System.out.println("How many " + teaName + " did you today?"); 
        if(input.hasNextInt() && (numberItem = input.nextInt()) > 0) { 
         istrue = false; 

         numberItem = input.nextInt(); 

        } 

       } catch (InputMismatchException e) { 
        input.nextLine(); 
        System.out.println("Please enter right number"); 
        istrue = true; 
       } 
       catch (NoSuchElementException e){ 
        System.out.println(" Please enter positive integers"); 
       } 
      } while (istrue); 

Answer 1

  do { 
      try { 
       System.out.println("How many " + teaName + " did you today?"); 
       if(input.hasNextInt()) { 
        if (numberItem = input.nextInt()) > 0) { 
         istrue = false; 

         numberItem = input.nextInt(); 
        } else { 
         throw new InputMisMatchException("negative num"); 
        } 

       } 

      } catch (InputMismatchException e) { 
       input.nextLine(); 
       System.out.println("Please enter right number"); 
       istrue = true; 
      } 
      catch (NoSuchElementException e){ 
       System.out.println(" Please enter positive integers"); 
      } 
     }while (istrue); 

這應該工作，我要做的就是拋出InputMismatchException時，當數字爲負。