Java的異常處理分配

Question

所以我最近了解到的異常處理Java和我還在努力去習慣它和所有，但我覺得我失去了一些東西。我爲我的課做了一個任務，編譯器不喜歡我的代碼。

我應該做一個計算器，它需要一個運算符，然後是一個數字，如果給定的運算符（+， - ，*，/）不是前面提到的四個運算符之一，那麼拋出異常。

我用的try-catch，但由於某些原因，try和catch不認識對方，除非我把它們彼此相鄰這是不是我真正想要的東西。

我的問題是真的：有沒有我的try和catch相互承認而不旁邊對方的方式，這樣我就可以在兩者之間它們運行的​​代碼？或者這是不可能的，我做的全部都是錯的？

這裏是我到目前爲止的代碼：

import java.util.*; 
public class Calculator 
{ 
     public static void main(String[] args) 
    { 
    String operatorInput; 
    double numberInput; 
    String userRedo = "Y"; 
    double result = 0.0; 
    Scanner input = new Scanner(System.in); 
    System.out.println("Type in an arithmetic operator of your choice and press enter."); 
    System.out.println("Then, please type in a number that will undergo the operation."); 

    while((userRedo.toUpperCase()).compareTo("Y")==0) 
    { 
     try 
     { 
      operatorInput = input.nextLine(); 
      if(operatorInput.compareTo("+")!=0||operatorInput.compareTo("-")!=0|| 
       operatorInput.compareTo("*")!=0||operatorInput.compareTo("/")!=0) 
      { 
       throw new UnknownOperatorException("Unknown operator!"); 
      } 
     } 

     numberInput = input.nextDouble(); 
     if(operatorInput.compareTo("+")==0) 
     { 
      result += numberInput; 
     } else if(operatorInput.compareTo("-")==0) 
     { 
      result -= numberInput; 
     } else if(operatorInput.compareTo("*")==0) 
     { 
      result = result * numberInput; 
     } else 
     { 
      result = result/numberInput; 
     } 

     System.out.println("\nresult "+operatorInput+" "+numberInput+"= "); 
     System.out.println("Updated result: "+result); 
     System.out.println("Again? (y/n)"); 
     userRedo = input.nextLine(); 


     catch(UnknownOperatorException e) 
     { 
      System.out.println(e.getMessage()); 
     } 
    } 
} 

}

和這裏的異常類我做：

public class UnknownOperatorException extends Exception 
    { 
public UnknownOperatorException() 
{ 
    super("Please select an actual operator and try again: "); 
} 

public UnknownOperatorException(String message) 
{ 
    super(message); 
} 

}

Answer 1

爲了try/catch語句工作正如Ghost在評論中所說，你需要把它們放在一起。

Answer 2

它們必須彼此相鄰。有幾件事情你可以做：

移動}在註釋行下來的方式，這樣

while((userRedo.toUpperCase()).compareTo("Y")==0) 
    { 
     try 
     { 
      operatorInput = input.nextLine(); 
      if(operatorInput.compareTo("+")!=0||operatorInput.compareTo("-")!=0|| 
       operatorInput.compareTo("*")!=0||operatorInput.compareTo("/")!=0) 
      { 
       throw new UnknownOperatorException("Unknown operator!"); 
      } 

     }//this one here 

採取這一併將其移動到這裏

System.out.println("\nresult "+operatorInput+" "+numberInput+"= "); 
    System.out.println("Updated result: "+result); 

}// put it here 

然後取這兩個行

System.out.println("Again? (y/n)"); 
userRedo = input.nextLine(); 

並將它們移動到下方：

 catch(UnknownOperatorException e) 
     { 
      System.out.println(e.getMessage()); 
     } 
     System.out.println("Again? (y/n)"); 
     userRedo = input.nextLine(); 
    } 
} 

這將讓你的while循環仍然有一些功能，並使你的try/catch工作。您可能需要調整的東西一點，使他們工作的權利，雖然

Answer 3

而且上面的代碼中存在一些問題......

也許這個作品。

public static void main(String[] args) { 
    String operatorInput=null; 
    double numberInput; 
    String userRedo = "Y"; 
    double result = 0.0; 
    Scanner input = new Scanner(System.in); 
    System.out.println("Type in an arithmetic operator of your choice and press enter."); 
    System.out.println("Then, please type in a number that will undergo the operation."); 

    while ((userRedo.toUpperCase()).compareTo("Y") == 0) { 
     try { 
      operatorInput = input.nextLine().trim(); 
      if (operatorInput.compareTo("+") != 0 
        && operatorInput.compareTo("-") != 0 
        && operatorInput.compareTo("*") != 0 
        && operatorInput.compareTo("/") != 0) { 
       throw new UnknownOperatorException("Unknown operator!"); 
      } 

     } catch (UnknownOperatorException e) { 
      System.out.println(e.getMessage()); 
      continue; 
     } 

     numberInput = Double.parseDouble(input.nextLine()); 

     if (operatorInput.compareTo("+") == 0) { 
      result += numberInput; 
     } else if (operatorInput.compareTo("-") == 0) { 
      result -= numberInput; 
     } else if (operatorInput.compareTo("*") == 0) { 
      result = result * numberInput; 
     } else { 
      result = result/numberInput; 
     } 

     System.out.println("\nresult " + operatorInput + " " + numberInput + "= "); 
     System.out.println("Updated result: " + result); 
     System.out.print("Again? (y/n) : "); 

     userRedo = input.nextLine(); 
    } 

    input.close(); 
}