Java main方法中的循环和异常处理

Question

我正在研究一个相当基本的问题：我正在编写一个Java程序，该程序接受一天，月份和年份的字符串（以整数形式，例如24/9/2015），然后将其转换为日期的基于单词的版本（例如2015年9月24日）。

我还需要能够通过创建我自己的异常类来处理用户从上面键入“无效”值的问题。

当引发异常时（例如，用户输入“无效”月份），程序应提示用户仅重新输入错误的值（因此，在这种情况下，它将提示用户仅重新输入月份）。

这是我到目前为止编写的代码（您可以假设异常类已经正确定义并且可以正常工作）：

import java.util.Scanner;

public class ParseDate {

public static void main(String args[]){

    String month, day, year;
    Scanner input = new Scanner(System.in);

    System.out.println("Enter the day: ");
    day = input.nextLine();
    System.out.println("Enter the month: ");
    month = input.nextLine();
    System.out.println("Enter the year: ");
    year = input.nextLine();

    try{
        formatDate(month, day, year);
    }
    catch(MonthException m){
        //?
    }
    catch(DayException d){
        //??
    }
    catch(YearException y){
        //???
    }
}

public static String formatDate(String month, String day, String year)
throws MonthException, DayException, YearException{
    String output;
    if (Integer.parseInt(month) < 1 || Integer.parseInt(month) > 12){
        throw new MonthException("Invalid month. reenter.");
    }
    if (Integer.parseInt(year) < 1000 || Integer.parseInt(year) > 3000){
        throw new MonthException("Invalid year. reenter.");
    }
    if (Integer.parseInt(day) < 1){
        throw new MonthException("Invalid day. reenter.");
        //extra code to handle the cases where the day is 
        //too large for the particular month and year entered
    }

    //other code here for converting date

    return output;
}
}

正如您可能从我的代码中看到的那样，我在确定应该在哪里以及如何使程序分别循环遍历异常时遇到麻烦。 我本来想使用switch但不太确定该在哪里放置switch 。

我怎样才能做到这一点？

Answer 1

因此，基本上，您需要某种方式来维护循环之间的信息，每次触发异常时，您只需要使与异常相关的信息无效即可。

然后，您需要继续循环直到所有值都经过验证并且可以格式化值为止，例如...

import java.util.Scanner;

public class ParseDate {

    public static void main(String args[]) {

        String day = null;
        String month = null;
        String year = null;
        String format = null;
        Scanner input = new Scanner(System.in);

        do {
            if (day == null) {
                System.out.println("Enter the day: ");
                day = input.nextLine();
            }
            if (month == null) {
                System.out.println("Enter the month: ");
                month = input.nextLine();
            }
            if (year == null) {
                System.out.println("Enter the year: ");
                year = input.nextLine();
            }

            try {
                format = formatDate(month, day, year);
            } catch (MonthException m) {
                System.err.println(month + " is not a valid month");
                month = null;
            } catch (DayException d) {
                System.err.println(day + " is not a valid day");
                day = null;
            } catch (YearException y) {
                System.err.println(year + " is not a valid year");
                year = null;
            }
        } while (format == null);
    }

    public static String formatDate(String month, String day, String year)
                    throws MonthException, DayException, YearException {
        String output = "Happy";

        int monthNum = 0;
        int dayNum = 0;
        int yearNum = 0;

        try {
            monthNum = Integer.parseInt(month);
            if (monthNum < 1 || monthNum > 12) {
                throw new MonthException("Invalid month. reenter.");
            }
        } catch (NumberFormatException exp) {
            throw new MonthException("Invalid month. reenter.");
        }
        try {
            yearNum = Integer.parseInt(year);
            if (yearNum < 1000 || yearNum > 3000) {
                throw new YearException("Invalid year. reenter.");
            }
        } catch (NumberFormatException exp) {
            throw new YearException("Invalid year. reenter.");
        }
        try {
            dayNum = Integer.parseInt(day);
            // You need to take into consideration the actual month,
            // but I'll leave that to you...
            if (dayNum < 1 || dayNum > 31) {
                throw new DayException("Invalid day. reenter.");
            }
        } catch (NumberFormatException exp) {
            throw new DayException("Invalid day. reenter.");
        }

        //other code here for converting date
        return output;
    }

    public static class MonthException extends Exception {

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

    }

    public static class DayException extends Exception {

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

    }

    public static class YearException extends Exception {

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

    }
}

坦率地说，现在单独验证每个对象会更简单，但这就是我