Java InputMismatchException错误

Question

我接到了一个任务，要做一些从ft和in到cm的转换。我已经记录了大部分内容，并且转换确实有效。我还希望在输入字符串或负数时包含A negative number...或A non-digit...语句，以显示所述消息。

我遇到的问题是，当我键入一个字符串或负数时，例如，当我输入-9时，我会得到testProgram.NegativeNumberException的输出。和testProgram.NonDigitNumberException，例如，当我输入joe时。

我认为catch中有问题，但不确定它不会点击的确切位置。

package testProgram;
import java.util.InputMismatchException;
import java.util.Scanner;

public class conversion{

   public static void main(String[] args) {
       Scanner scan = new Scanner(System.in);
       double cm = -1;
       while(cm == -1){
       cm = convertToCentimeters(scan);

       if(cm!=-1){
       System.out.println("Your result = " +cm);
       }
       else{
           System.out.println("Please enter the values again.");
       }
       scan.nextLine();
       }
   }
   public static double convertToCentimeters(Scanner scan){
       double centimeters = -1;
       try{
           double foot = getFootValue(scan);
           double inch = getInchValue(scan);
           double totalInches = foot * 12 + inch;
           centimeters = totalInches * 2.54;

           }catch(NegativeNumberException e1){
               System.out.println(e1);
           }
           catch(NonDigitNumberException e2){
               System.out.println(e2);
           }
           return centimeters;
   }
   public static double getFootValue(Scanner scan) throws NegativeNumberException, NonDigitNumberException{
       try{
       System.out.println("Enter the foot value: ");
       double foot = scan.nextDouble();
       if(foot <= 0){
           throw new NegativeNumberException ("A negative foot value has been entered.");
       }
       return foot;
       }
       catch(InputMismatchException e){
           throw new NonDigitNumberException ("A non-digit foot value has been entered.");
       }
   }
   public static double getInchValue(Scanner scan)throws NegativeNumberException, NonDigitNumberException{
   try{
       System.out.println("Enter the inch value: ");
       double inch = scan.nextDouble();
       if(inch <= 0){
           throw new NegativeNumberException ("A negative inch value has been entered.");
       }
       return inch;
       }
       catch(InputMismatchException e){
           throw new NonDigitNumberException ("A non-digit inch value has been entered.");
       }
   }
}

Answer 1

作为@Scary建议的替代方案，您可以将构造函数添加到自定义异常中，如下所示-

NegativeNumberException(String str) {
    System.out.println(str);
}

这将帮助您在以下情况下打印消息

throw new NegativeNumberException ("A n....");