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所以我们必须做一个抵押计算项目，我们必须要求用户再次计算，现在我们必须让它在每次用户输入任何输入的字符串值时打印出错误消息。我认为我做对了，但是每次运行它时都会发生一些奇怪的事情，我不知道为什么，我知道 Try-Catch 块有问题。

这是我的输出：http: //imgur.com/cbvwM5v

正如您所看到的，第三次运行程序时，我输入了“二”作为第二个输入，它仍然进行了计算。然后，第三次尝试时，我输入了一个负数，然后输入了一个“2”，一切都按照我想要的方式进行。然后，我最后一次运行它时，我为第一个输入输入了一个正数，它仍然进行计算，你们看到的任何东西可能会这样做吗？另外，我想我可能使用了错误的异常，我不确定这意味着什么，我只是猜测。我应该用户 NumberFormatException 并且在 nfe 下还有一行说该值没有被使用。

这是我的代码：

   package MortgageCalculation2c;

import java.text.NumberFormat;
import java.util.Scanner;
/**
 *
 * @author Akira
 */
public class MortgageCalculation2c {

/**
 * @param args the command line arguments
 */
public static void main(String[] args) {
     Scanner in = new Scanner(System.in);


    double loanAmount = 0;
    double interestRate = 0;
    double numberYears = 0;
    double months;
    double monthlyPayment;
    double numerator;
    double denominator;
    double formula;
    boolean userInput = true;
    String answer = ("y");


    while (userInput) {
        try {
            loanAmount = 0;
            interestRate = 0;
            numberYears = 0;

   //prompt user for the loan amount       
    System.out.print("Enter the loan amount: ");
    loanAmount = Double.parseDouble(in.nextLine());

    //prompt the user for the interest rate
    System.out.print("Enter the rate: ");
    interestRate = Double.parseDouble(in.nextLine());

    //prompt the user for  thenumber of years
    System.out.print("Enter the number of years: ");
    numberYears = Double.parseDouble(in.nextLine());

        } catch (NumberFormatException nfe) {
            System.out.println("You must enter positive numerical data!");
        }


    //if the user enters a negative number print out a error message, if not, continue calculations
   if ((loanAmount <= 0) || (interestRate <= 0) || (numberYears <= 0)) {
        System.out.println("ALL NUMERICAL VALUES MUST BE POSITIVE!");

    } else {
        //convert the interest rate
       interestRate = interestRate / 100 / 12;

       //the number of years must be converted to months
       months = numberYears * 12;

       //numerator of the monthly payment formula
       numerator = (Math.pow(1 + interestRate, months));

       //denominator of the monthly payment formula
       denominator = ((numerator)-1);

       //the formula equals the numerator divided by the denominator
       formula = ( numerator / denominator );

       //monthly payment calculation
        monthlyPayment = (interestRate * loanAmount * formula);

         //sytem output
        NumberFormat defaultFormat = NumberFormat.getCurrencyInstance();
        System.out.println("The monthly payment is: " + defaultFormat.format(monthlyPayment));

   }

        //prompt the user if they would like to calculate the program again.
        System.out.println("Would you like to calculate again (y/n) : ");

        //if the user enters "y" the program will run again and if the user enters anything else it ends
            answer = in.nextLine();
        answer = answer.toLowerCase();
            if ( answer.equals("y")){
                userInput = true;  //tests the program if it needs to run again
            }else{
                break;  //ends the program
            }

}

}
}

你们有什么可以看到的可能是问题的地方吗？

4

1 回答 1

0

看来你需要continue在你的catch块中，所以程序流程回到循环。

    ...
    } catch (NumberFormatException nfe) {
        System.out.println("You must enter positive numerical data!");
        continue;   // <---------- here
    }
    ...

如果这不是try-catch构造中的特定练习，最好使用Scanner' 方法hasNextDouble()来验证以及nextDouble读取和转换数字。

它看起来像这样：

//prompt user for the loan amount       
loanAmount = enterPositiveDouble("Enter the loan amount: ")

//prompt the user for the interest rate
interestRate = enterPositiveDouble("Enter the rate: ");

//prompt the user for  the number of years
numberYears = enterPositiveDouble("Enter the number of years: ");

你将有一个特殊的static方法enterPositiveDouble，如下所示：

static void  enterPositiveDouble(String prompt) {
   Scanner in = new Scanner(System.in);
   boolean ok = true;
   double result = -1; 
   do {
      System.out.print(prompt);
      ok = (in.HasNextDouble() && (result = in.NextDouble()) > 0)
      if ! ok
         System.out.println("You must enter positive numerical data!");
   } while (!ok); 
}

以上不是最佳代码，而只是可能解决方案的说明。

于 2013-10-30T13:07:31.993 回答