java - 为什么我的二进制到十进制转换程序读不到 0？

Question

该程序应该将二进制数转换为十进制数，并在输入有非二进制数时抛出异常。这个程序会读取1，但是当我输入0时，它会抛出异常并告诉我它不是二进制。

测试程序:

   //Prepare scanner from utility for input.
   import java.util.Scanner;

   public class Bin2Dec {
       public static void main (String[] args){
       //Convert the input string to their decimal equivalent.
        //Open scanner for input.
        Scanner input = new Scanner(System.in);
        //Declare variable s.
        String s;

        //Prompt user to enter binary string of 0s and 1s.
        System.out.print("Enter a binary string of 0s and 1s: ");
        //Save input to s variable.
        s = input.nextLine();
            //With the input, use try-catch blocks.
            //Print statement if input is valid with the conversion.
            try {
             System.out.println("The decimal value of the binary number "+ "'" + s + "'" +" is "+conversion(s));
             //Catch the exception if input is invalid.
              } catch (BinaryFormatException e) {
                  //If invalid, print the error message from BinaryFormatException.
                System.out.println(e.getMessage());
              }
            }
          //Declare exception.
          public static int conversion(String parameter) throws BinaryFormatException {
            int digit = 0;
            for (int i = parameter.length(); i > 0; i--) {
              char wrong_number = parameter.charAt(i - 1);
              if (wrong_number == '1') digit += Math.pow(2, parameter.length() - i);
              //Make an else statement and throw an exception.
              else 
                  throw new BinaryFormatException("");
            }
            return digit;
          } 
        }

异常程序:

    public class BinaryFormatException extends Exception {
        //Declare message.
          private String message;
          public BinaryFormatException(String msg) {
            this.message = msg;
          }
          //Return this message for invalid input to Bin2Dec class.
          public String getMessage() {
             return "Error: This is not a binary number";
          }
        }

Answer 1

如果 char 不是 1，则抛出 BinaryFormatException 异常。

       if (wrong_number == '1') digit += Math.pow(2, parameter.length() - i);
          //Make an else statement and throw an exception.
          else 
              throw new BinaryFormatException("");