如何从同一实例获得另一个日历结果？

Question

    public static ArrayList  listOfHolidays = new ArrayList();

        Holidays.holidaysList.add(new Holidays("Sukkot", "09/10/2014"));
        Holidays.holidaysList.add(new Holidays("Hanukkah", "17/12/2014"));
        Holidays.holidaysList.add(new Holidays("Purim", "16/03/2014"));

    Calendar calendar = Calendar.getInstance();

    @Override
    public String toString() {
    //DayOfWeek is just an enum of days (strings)
        return holidayName + " falls on "
                    + DayOfWeek.values()[Calendar.DAY_OF_WEEK - 1]; // Here i get the same day each time
    }

    @Override
        public int compareTo(Holidays another) {
            if(MainActivity.sortByName == true) {
                    return holidayName.compareToIgnoreCase(another.holidayName);
            }
            return convertStringToCal() - another.convertStringToCal();
        }

        private int convertStringToCal() {
            int year, month, day;
            day = Integer.valueOf(holidayDate.substring(0, 2));
            month = Integer.valueOf(holidayDate.substring(3, 5));
            year = Integer.valueOf(holidayDate.substring(6, 10));
            calendar = Calendar.getInstance();
            calendar.set(year, month, day);
            return (int) calendar.getTimeInMillis();
        }

Collections.sort()

Answer 1

我认为它可能行不通有多种原因。

首先，我不知道您是否省略了Holidays类的部分代码，但实际上从未将calendar对象设置在convertStringToCal（）方法之外，但我不知道构造函数中是否也调用了这个方法。

其次也是最有可能是你的问题：

@Override
    public String toString() {
    //DayOfWeek is just an enum of days (strings)
        return holidayName + " falls on "
                                        // Here you are using the constant Calendar.DAY_OF_WEEK
                    + DayOfWeek.values()[Calendar.DAY_OF_WEEK - 1]; // Here i get the same day each time
    }

它实际上应该是这样的：

@Override
    public String toString() {
    //DayOfWeek is just an enum of days (strings)
        return holidayName + " falls on "
                    + DayOfWeek.values()[calendar.get(Calendar.DAY_OF_WEEK)]; // Now you won't get the same day every time. :)
    }

一些附加说明：

我将使用date对象保存日期，并使用simpledateformat将字符串转换为日期，反过来也可以。

public class Holidays {

        private final Calendar calendar = Calendar.getInstance();
        private final String holidayName;

        public Holidays(String holidayName, Date date) {
            this.holidayName = holidayName;
            this.calendar.setTime(date);
        }

        @Override
        public int compareTo(Holidays another) {
            // Generally you should avoid passing information statically between Activities
            if(MainActivity.sortByName == true) {
                    return holidayName.compareToIgnoreCase(another.holidayName);
            }
            return getTimeInMillis() - another.getTimeInMillis();
        }

        public long getTimeInMillis() {
            return this.calendar.getTimeInMillis();
        }

        @Override
        public String toString() {
        //DayOfWeek is just an enum of days (strings)
            DayOfWeek day = DayOfWeek.values()[calendar.get(Calendar.DAY_OF_WEEK)]; // Now you won't get the same day every time. :)
            return String.format("%s falls of %s", this.holidayName, day);
        }

    }

// Create date objects with calendar.
Calendar calendar = Calendar.getInstance();
calendar.set(Calendar.YEAR, 2014);
calendar.set(Calendar.MONTH, 3);
calendar.set(Calendar.DAY_OF_MONTH, 27);
Date date = calendar.getTime();

通过SimpleDateFormat，您可以转换String和Date对象，如下所示：

// The String pattern defines how date strings are parsed and formated
SimpleDateFormat sdf = new SimpleDateFormat("dd/MM/yyyy");

String dateString = "09/10/2014";

// Convert a String to Date
Date dateFromDateString = sdf.parse(dateString);

// Convert a Date to a String
String dateStringFromDate = sdf.format(dateFromDateString);

如果您需要的不仅仅是date和string对象的简单转换，那么您可以使用dateformat。这几乎是日期字符串转换的劳斯莱斯。它可以以一种更通用的方式解析和格式化字符串，而实际上不需要模式，并且它自动地考虑区域设置等等。

或者您可以使用JodaTime：）