Java dates

Java dates

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  Java Dates Sujit Kumar ZenolocityLLC Copyright @
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  java.util.Date • Represents aninstant in time • Signed long representing number of millisecs since epoch • Epoch based. Epoch is Jan 01, 1970 00:00:00 GMT • Date() constructor creates a date object representing the current time • Date(long) constructor creates a date object representing that time. System.currentTimeMillis() returns the current epoch based time.
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  Date Methods Comparison Methods: •after(Date) • before(Date) • compareTo(Date) • equals(Date) Note: Lot of deprecated methods in Date. Use Calendar class and it’s methods instead.
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  java.sql.Date • Java.util.Date isa basic, all-purpose Date object. It simply stores a Date (as a long) and allows you to display it. java.sql.Date extends java.util.Date to add the following functionality: 1) toString outputs the date as "yyyy-mm-dd" instead of as a Locale specific String. 2) add the valueOf method to read a String of "yyyymm-dd" format and parse it into a java.sql.Date object.
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  java.util.Calendar • Represents aspecific instance in time • Abstract class – it’s concrete derived classes support different calendar styles. • Gregorian Calendar most common implementation • Calendar.getInstance() returns a localized Calendar object initialized with current date and time.
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  Calendar (contd…) • setand get each of the date and time fields like month, day, year, hour, minutes, seconds, etc. • Compare calendar objects using before, after and compareTo. • Date and time arithmetic with the add method. • Use getTime() to convert to a Date object.
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  java.util.TimeZone • Represents atimezone offset, calculates the daylight savings time as well. • TimeZone.getTimeZone() method returns a TimeZone object based on the system’s time zone setting. • TimeZone.getTimeZone("America/Los_Angeles") to get the TimeZone object for a specific timezone ID. • Invoke the getTimeZone() method on a calendar object to return the corresponding TimeZone object. • Important methods: getId(), getDisplayName() and getRawOffset()
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  Format and ParseDates • java.text.DateFormat : abstract class • The format(Date) method generates a String representation of a Date object • The parse(String) method generates a Date object by parsing a date/time string • Java.text.SimpleDateFormat – concrete class for user defined patterns for formatting & parsing dates and times.
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  Thread Safe SimpleDateFormat • SimpleDateFormatis not thread safe. • Here is an implementation to make it thread safe. public class ThreadSafeSimpleDateFormat { private DateFormat df; public ThreadSafeSimpleDateFormat(String format) { this.df = new SimpleDateFormat(format); } public synchronized String format(Date date) { return df.format(date); } } public synchronized Date parse(String string) throws ParseException { return df.parse(string); }
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  DateFormat Static Methods •Static methods to obtain date/time formatters. • Based on the default or a specific locale. • Examples: DateFormat.getDateTimeInstance() DateFormat.getDateInstance( DateFormat.LONG, Locale.GERMAN) DateFormat.getTimeInstance(DateFormat.LONG)
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  Joda-time • High qualityreplacement for the Java date and time classes. • Design allows for multiple calendar systems, while still providing a simple API. The 'default' calendar is the ISO8601 standard which is used by XML. • The Gregorian, Julian, Buddhist, Coptic, Ethiopic and Islamic systems are also included. • Supporting classes include time zone, duration, format and parsing. • http://joda-time.sourceforge.net/