Java中的異常後重新提示

Question

我記得在Python中有這個確切的問題。這個Java代碼是我的Python代碼的一個副本，用於計算三角形的面積。如果輸入一個非數字值，我會發現一個異常，但最終的結果會被打亂。

private static float baseLength() { 
    float baseLength = 0; 
    Scanner user_input = new Scanner(System.in); 
    try { 
     while (baseLength <= 0) { 
      System.out.print("Enter the base length of the triangle: "); 
      baseLength = user_input.nextFloat(); 
      if (baseLength <=0) { 
       System.out.println("Error. Plase enter a number higher than 0."); 
      } 
     }    
    } catch (InputMismatchException badChar) { 
     System.err.println("You have entered a bad value. Please try again"); 
     baseLength(); 
    } 
    return baseLength; 

它將從錯誤的數字中恢復，但不是從不是數字的值中恢復。我仍然無法弄清楚確切的問題是什麼。

Answer 1

與System.err的

private static float baseLength() { 
    float baseLength = 0; 

    while (true) 
    { 
    try { 
     System.out.print("Enter the base length of the triangle: "); 

     Scanner user_input = new Scanner(System.in); 
     baseLength = user_input.nextFloat(); 

     if (baseLength>0) 
      return baseLength; 

     if (baseLength <=0) 
       System.err.println("Error. Plase enter a number higher than 0."); 
     } 
     catch (InputMismatchException badChar) 
     { 
     System.err.println("You have entered a bad value. Please try again"); 
     } 
    } 
} 

測試更加清晰，和主迴路內的異常，和每一個錯誤

Answer 2

你可以把while環周圍的try/catch塊來實現這一目標：

private static float baseLength() { 
    float baseLength = 0; 
    Scanner user_input = new Scanner(System.in); 
    while (baseLength <= 0) { 
     try { 
      System.out.print("Enter the base length of the triangle: "); 
      baseLength = user_input.nextFloat(); 
      if (baseLength <= 0) { 
       System.out.println("Error. Plase enter a number higher than 0."); 
      } 
     } catch (InputMismatchException badChar) { 
      System.err.println("You have entered a bad value. Please try again"); 
     } 
    } 
    return baseLength; 
}