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George Wilkinson
2024-03-08 10:55:57 +00:00
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commit 68fa81d02f
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Semester 2/Programming 2/Project/Part 2/DateUtil.java Normal file
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import java.text.SimpleDateFormat;
import java.text.ParseException;
import java.text.ParsePosition;
import java.util.Date;
import java.util.Calendar;
import java.util.GregorianCalendar;
/**
*
* A class DateUtil with the following methods for dealing with dates.
*
* public static String convertDateToLongString(Date date)
* public static String convertDateToShortString(Date date)
* public static Date convertStringToDate(String dateString)
* public static int daysBetween(Date startDate, Date endDate)
* public static Date incrementDate(Date date, int noOfDays)
* public static boolean isLeapYear(int year)
* public static boolean isValidDateString(String dateString)
* public static Date nextDate(Date date)
*
* @author D E Newton
*
*/
public class DateUtil
{
public static SimpleDateFormat dateFormatter;
private static String longDatePattern;
private static String shortDatePattern;
/**
* initializer block -- useful for
* initializing static fields
*/
static
{
shortDatePattern = "dd-MM-yyyy"; // dd = day, MM = month, yyyy = year (as 2, 2 and 4 digits respectively)
longDatePattern = "EEEE, d MMMM yyyy"; // e.g. Saturday, 25 March 2023
// EEEE (4 or more) = day in week, in full e.g.Saturday
// MMMMM (4 or more) = month name as text in full e.g. March
// d = day as 1 or 2 digits e.g. 25th of month -> 25, 23rd -> 23
//
// some alternatives below to help understanding (see documentation for SimpleDateFormat class)
// EE (3 or less) -> Tue
// MMMM = month name as text in short e.g. Oct
// M (or MM) = month as digits e.g. 1 (or 01) would correspond to January
dateFormatter = new SimpleDateFormat(shortDatePattern); // default pattern set
dateFormatter.setLenient(false); // default is true and impossible dates such
// as 31-09-2023 would be accepted but interpreted as 01-10-2023
}
/**
* Converts a Date object to a corresponding String in
* the long date pattern style "Saturday, 25 March 2023".
*
* @param date a Date object
*
* @return a String, containing a long date pattern
*/
public static String convertDateToLongString(Date date)
{
dateFormatter.applyPattern(longDatePattern);
String dateString = dateFormatter.format(date);
dateFormatter.applyPattern(shortDatePattern); // reset pattern
return dateString;
}
/**
* Converts a Date object to a corresponding String in
* the short date pattern style "25-03-2023".
*
* @param date a Date object
*
* @return a String, containing a short date pattern
*/
public static String convertDateToShortString(Date date)
{
return dateFormatter.format(date);
}
/**
* Converts a string in the short date pattern style "25-03-2023"
* to a corresponding Date object.
*
* Any leading or trailing spaces are first removed from the date string.
* The String parameter that represent a date as a string must be in the
* format dd-mm-yyy (e.g. 25-03-2023 or 25-3-2023) where dd represents
* one or two digits representing the day in the month, similarly for
* mm representing the month in the year and yyyy represents the four
* digits for the year.
*
* A RuntimeException is thrown if the date string is not recognised as
* a valid date. Such exceptions do not need to be caught or thrown as
* they are unchecked exceptions, but can be caught if necessary.
*
* @param dateString a Date object
*
* @return the Date object
*/
public static Date convertStringToDate(String dateString)
{
dateString = dateString.trim();
ParsePosition posn = new ParsePosition(0); // initialise posn to the beginning of the string to be parsed
Date date = dateFormatter.parse(dateString, posn);
int endIndex = posn.getIndex(); // posn after parsing
String message = "Date string <" + dateString + "> not recognised";
if( date==null )
{
// parsing failed because string not recognised
message += ".";
throw new RuntimeException(message);
}
else if( endIndex!=dateString.length() )
{
// parsing failed because parsing did not "consume" all the characters
// in the string, indicating the complete string was not recognised
message += " because it contains extra characters after a date.";
throw new RuntimeException(message);
}
else
return date;
}
/**
* Calculates the number of days between two given dates, startDate and endDate.
*
* If startDate is after endDate then the number of days returned will be negative.
*
* @param startDate a Date object
* @param endDate a Date object
*
* @return an int, number of days between the dates
*/
public static int daysBetween(Date startDate, Date endDate)
{
// first check that startDate is not after endDate
boolean outOfOrder;
Date temp;
if( startDate.compareTo(endDate)<=0 )
{
outOfOrder = false;
}
else
{
outOfOrder = true;
temp = startDate;
startDate = endDate;
endDate = temp;
}
int daysBetween = 0;
Calendar calendar = new GregorianCalendar();
calendar.setTime(startDate); // initialised at start date
Calendar calendarEndDate = new GregorianCalendar();
calendarEndDate.setTime(endDate);
// First advance calendar a year at a time without advancing past the end date.
// This is much quicker, for dates that are years apart, than simply relying on the
// later "day at a time" loop. Advancing "a month at a time" before the "day at a
// time" loop would be even better but complex because of the varying month lengths.
Calendar prevYearCalendar = (Calendar) calendar.clone();
calendar.add(Calendar.YEAR, 1);
// advance calendar a year at a time until end date reached
while( !calendar.getTime().after(endDate) )
{
if( isLeapYear(prevYearCalendar.get(Calendar.YEAR)) &&
prevYearCalendar.get(Calendar.MONTH)<Calendar.MARCH )
// advancing past a leap year day
daysBetween += 366;
else
daysBetween += 365;
prevYearCalendar = (Calendar) calendar.clone();
calendar.add(Calendar.YEAR, 1);
}
calendar = prevYearCalendar; // calendar always advances too far, so need to correct
// now advance calendar a day at a time until end date reached
while( calendar.getTime().before(endDate) )
{
calendar.add(Calendar.DAY_OF_MONTH, 1);
daysBetween++;
}
if( outOfOrder )
daysBetween = -daysBetween;
return daysBetween;
}
/**
* Given date, a Date object, and noOfDays, an int, the method returns
* a Date object corresponding to noOfDays later than date.
*
* If noOfDays is negative, the resulting Date object will be before date.
*
* @param date a Date object
* @param noOfDays an int
*
* @return a Date
*/
public static Date incrementDate(Date date, int noOfDays)
{
Calendar calendar = new GregorianCalendar();
calendar.setTime(date);
calendar.add(Calendar.DAY_OF_MONTH, noOfDays);
return calendar.getTime();
}
/**
* Given year, an int, the method checks to see if the year
* is a leap year.
*
* @param year, an int
*
* @return a boolean, true only if the year is a leap year.
*/
public static boolean isLeapYear(int year)
{
GregorianCalendar calendar = new GregorianCalendar();
return calendar.isLeapYear(year);
}
/**
* Given dateString, a String, the method checks to see if string
* corresponds to a valid shortDatePattern.
*
* @param dateString, a String
*
* @return a boolean, true only if the dateString is a valid pattern
*/
public static boolean isValidDateString(String dateString)
{
try
{
Date d = DateUtil.convertStringToDate(dateString);
return true;
}
catch(RuntimeException ex)
{
return false;
}
}
/**
* Given date, a Date object, the method returns
* a Date object corresponding to the next day.
*
* @param noOfDays an int
*
* @return a Date
*/
public static Date nextDate(Date date)
{
return incrementDate(date, 1);
}
}