001 package edu.nrao.sss.util;
002
003 import java.text.DateFormat;
004 import java.text.SimpleDateFormat;
005 import java.util.Calendar;
006 import java.util.Date;
007 import java.util.TimeZone;
008
009 /**
010 * A helper class for working with {@link java.util.Date dates}.
011 * <p>
012 * <b>Version Info:</b>
013 * <table style="margin-left:2em">
014 * <tr><td>$Revision$</td></tr>
015 * <tr><td>$Date$</td></tr>
016 * <tr><td>$Author$ (last person to modify)</td></tr>
017 * </table></p>
018 *
019 * @author David M. Harland
020 * @since 2007-09-19
021 */
022 public class DateUtility
023 {
024 private static final Calendar CALENDAR = Calendar.getInstance();
025 private static final Date LOW_DATE;
026 private static final Date HIGH_DATE;
027
028 static
029 {
030 CALENDAR.clear();
031 CALENDAR.setTimeZone(TimeZone.getTimeZone("GMT"));
032
033 //Sept 14, 1752 (adoption of Gregorian by England & colonies)
034 CALENDAR.set(1752, 8, 14, 0, 0, 0);
035 LOW_DATE = CALENDAR.getTime();
036
037 //Dec 31, 9999
038 CALENDAR.set(9999, 11, 31, 0, 0, 0);
039 HIGH_DATE = CALENDAR.getTime();
040 }
041
042 /**
043 * Creates and returns a very low, or early, date.
044 * <p>
045 * This date is prior to any
046 * date that would reasonably be used in NRAO's SSS software.
047 * For the curious, this date is currently set to
048 * September 14, 1752, but no code should rely on this.
049 * (This is the first date that England and her colonies
050 * used the Gregorian Calendar.)</p>
051 */
052 public static Date createEarlyDate()
053 {
054 //Dates are mutable, so we can't pass out the actual variable
055 return (Date)LOW_DATE.clone();
056 }
057
058 /**
059 * Creates and returns a very high, or late, date.
060 * <p>
061 * This date is after any
062 * date that would reasonably be used in NRAO's SSS software.
063 * For the curious, this date is currently set to
064 * December 31, 9999, but no code should rely on this.</p>
065 */
066 public static Date createLateDate()
067 {
068 //Dates are mutable, so we can't pass out the actual variable
069 return (Date)HIGH_DATE.clone();
070 }
071
072 /**
073 * Returns <i>true</i> if this utility's
074 * {@link #createEarlyDate() earlyDate} is equal to
075 * {@code yourDate}.
076 * <p>
077 * Using this method is more efficient that calling
078 * <tt>DateUtility.createLateDate().equals(yourDate)</tt>
079 * because this method creates no new objects.</p>
080 *
081 * @param yourDate the date to be tested.
082 *
083 * @return <i>true</i> if your date is the early date.
084 */
085 public static boolean earlyDateEquals(Date yourDate)
086 {
087 return LOW_DATE.equals(yourDate);
088 }
089
090 /**
091 * Returns <i>true</i> if this utility's
092 * {@link #createEarlyDate() earlyDate} is equal to
093 * {@code yourDate}.
094 * <p>
095 * Using this method is more efficient that calling
096 * <tt>DateUtility.createLateDate().equals(yourDate)</tt>
097 * because this method creates no new objects.</p>
098 *
099 * @param yourDate the date to be tested.
100 *
101 * @return <i>true</i> if your date is the early date.
102 */
103 public static boolean lateDateEquals(Date yourDate)
104 {
105 return HIGH_DATE.equals(yourDate);
106 }
107
108 /**
109 * Creates and returns a date formatter than parses dates from, and
110 * writes dates to,
111 * <a href="http://en.wikipedia.org/wiki/ISO_8601">ISO 8601</a> text.
112 *
113 * @return
114 * a date formatter built around the ISO 8601 specification.
115 */
116 public static DateFormat makeIso8601Formatter()
117 {
118 return new SimpleDateFormat(FormatString.ISO8601_DATE_TIME_TIMEZONE);
119 }
120 }