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The Java programming language provides the Date class offered in the java.util package; this class encapsulates the present date and time.
- The Date class supports two constructors as shown in the following table.
|No.||Constructor and Description td>|
|1|| Date () |
This constructor initializes an object with the current date and time. td>
|2|| Date (long millisec) |
This constructor takes an argument equal to the number of milliseconds that have elapsed since midnight on January 1, 1970 td>
Date class methods
- Below are the methods of the Date class.
|No.||Methods with a description|
|1|| boolean after (Date date)
Returns true if the calling date object contains a date that is later than the specified date, otherwise it returns false.
|2|| boolean before (Date date)
Returns true if the calling date object contains a date earlier than the specified date, otherwise it returns false.
|3|| Object clone ()
Duplicate the calling object date.
|4|| int compareTo (Date date)
Compares the value of the calling object with this date. Returns 0 if the values are equal. Returns a negative value if the call object is earlier than the date. Returns a positive value if the call object is later than the date.
|5|| int compareTo (Object obj)
Works exactly the same compareTo (Date) if the call object has a Date class. Otherwise, it calls ClassCastException.
|6|| boolean equals (Object date)
Returns true if the calling date object contains similar time as well as date which are specified in date, or else it returns false.
|7|| long getTime ()
Returns the number of milliseconds that elapsed since January 1, 1970.
|8|| int hashCode ()
Returns the hash code for the calling object.
|9|| void setTime (long time)
Sets the date and time corresponding to the time point, which represents the total time spent in milliseconds from midnight on January 1, 1970.
|10|| String toString ()
Converts the calling date object to a string and returns the result.
Current date and time in Java
- Getting the current date and time in Java is not hard enough. You can use a simple date object with the toString () method to display the current date and time as follows:
Following are the three ways to compare two dates −
- You can use the getTime () function to get the number of milliseconds that have elapsed since midnight on January 1, 1970, for both objects, and then compare these two values.
- You can use the methods before (), after (), and equals (). Since the 12th of the month is earlier than the 18th date, for example, new Date (99, 2, 12) .before (new Date (99, 2, 18)) returns true.
- You also use compareTo () method, that is defined by a comparable interface and then implemented by date.
Formatting a Date with SimpleDateFormat
SimpleDateFormat is a concrete class for parsing and formatting dates in Java. SimpleDateFormat allows you to start by selecting any custom templates for formatting the date and time. For example:
SimpleDateFormat format codes
- To specify the time format, use a time pattern string. In this pattern, all the ASCII letters are reserved as pattern letters, that are defined as the following −
|G||The era designation||AD|
|M||Month of the year number||11|
|d||Number of the month||13|
|h||Hour format in A.M./P.M. (1 ~ 12)||7|
|H||Hour format (0 ~ 23)||19|
|E||Day of the week||Sun|
|D||Number of the day of the year||318|
|F||The day of the week in the month||2 (the second Sunday in this month)|
|w||Week number in the year||46|
|W||The week number in the month||2|
|k||Hour format (1 ~ 24)||24|
|K||Hour format in A.M./P.M.(0~11)||0|
|z||Time Zone||FET (Far Eastern European Time)|
|'||Highlighting for text||Text|
|''||Single quotation mark||'|
Date Formatting Using printf
- The format of the date and time can be made easily with the printf method. You use a two-letter format, starting with t and ending with one of the symbols in the table below. For example:
- It would be a bit silly if you would have to put the date several times to format each part. For this reason, the string format can indicate the argument index for formatting.
The index should directly follow% and terminate $. For example:
- In addition, you can use < This means that the same argument should be used again, like the previous format specifications. For example:
Date and Time Conversion Characters
- In Java, you can implement the date output in the correct format using the following conversion characters:
|c||Current time and date||Sun Nov 13 01:19:27 FET 2016|
|F||Date format ISO 8601 (year-month-day)||2016-11-13|
|D||American date format (month / day / year)||11/13/16|
|T||24-hour time format||01:26:09|
|r||12-hour time format||01:26:51 AM|
|R||24-hour time format without seconds||01:27|
|Y||Current year of four digits (with leading zeros)||2016|
|y||Last two digits of the year (with leading zeros)||16|
|C||The first two digits of the year (with leading zeros)||20|
|B||Full month name||November|
|b||Abbreviated month name||Nov|
|m||Current month number (with leading zeros)||11|
|d||The number of the current day of the month (with leading zeros)||09|
|e||The number of the current day of the month (without leading zeros)||9|
|A||The full name of the current day of the week||Sunday|
|a||Abbreviated day of the week||Sun|
|j||Number of days since the beginning of the year (with leading zeros)||318|
|H||Hour format (with leading zeros), from 00 to 23||01|
|k||Hour format (without leading zeros), from 0 to 23||1|
|I||Hour format (with leading zeros), from 01 to 12||01|
|l||Hour format (without leading zeros), from 1 to 12||1|
|M||Minutes (with leading zeros)||38|
|S||Seconds (with leading zeros)||50|
|L||Milliseconds (with leading zeros)||382|
|N||Nanoseconds (with leading zeros)||775000000|
|p (% Tp)||The upper register of the marker is A.M./P.M.||AM|
|p (% tp)||Lowercase of the marker A.M./P.M.||am|
|z||Hourly offset RFC 822 by GMT||+0300|
|s||Seconds since 1970-01-01 00:00:00 GMT||1478991147|
|Q||Milliseconds since 1970-01-01 00:00:00 GMT||1478991172134|
Converting a string to a date
- The SimpleDateFormat classes have some other methods, notably parse( ), that tries to parse a string along with the format stored in the given SimpleDateFormat object.
- You can increase or decrease the running time of the program for any period of time, from one millisecond to the life of your computer. For example, the following program will be in standby mode for 10 seconds:
- nstead of Thread.sleep (), we recommend using TimeUnit (): TimeUnit.NANOSECONDS.sleep (), TimeUnit.MICROSECONDS.sleep (), TimeUnit.MILLISECONDS.sleep (), TimeUnit.SECONDS.sleep (), TimeUnit.MINUTES.sleep ( ), TimeUnit.HOURS.sleep (), or TimeUnit.DAYS.sleep ().
- The GregorianCalendar is concrete implementation of Calendar class which implements the ordinary Gregorian calendar with that you are well-known.
- A getInstance( ) method of a Calendar returns the GregorianCalendar which are started with present date and time in a default locale as well as time zone.
- GregorianCalendar defines two fields. They are AD and BC and represents through two eras which are defined by Gregorian calendar.
There are numerous constructors for GregorianCalendar objects. They are −
|No.||Constructor and its description|
|1|| GregorianCalendar ()
Creates a GregorianCalendar value, using the default current date and time, localization, and time zone.
|2|| GregorianCalendar (int year, int month, int date)
Creates GregorianCalendar according to the specified date in the time zone and the default localization.
|3|| GregorianCalendar (int year, int month, int date, int hour, int minute) |
Creates GregorianCalendar according to the specified date and time in the time zone and the default localization. td >
|4|| GregorianCalendar (int year, int month, int date, int hour, int minute, int second)
Creates GregorianCalendar according to the specified date and time in the time zone and the default localization.
|5|| GregorianCalendar (Locale aLocale)
Creates GregorianCalendar according to the current time in the default time zone within the specified localization.
|6|| GregorianCalendar (TimeZone zone)
Constructs the GregorianCalendar based on the present time in a given time zone with default localization.
|7|| GregorianCalendar (TimeZone zone, Locale aLocale)
Constructs a GregorianCalendar based on the current time in a given time zone and localization.
A list of several useful methods provided by the GregorianCalendar class:
|No.||Methods with a description|
|1|| void add (int field, int amount)
Adds the specified amount of time to this temporary field along with the calendar rules.
|2|| protected void computeFields ()
Converts the GMT time in milliseconds to the value of the time fields.
|3|| protected void computeTime ()
Converts the values of the temporary Calendar field to UTC format in milliseconds.
|4|| boolean equals (Object obj)
Compares this GregorianCalendar to a reference object.
|5|| int get (int field)
Gets the value for the specified time field.
|6|| int getActualMaximum (int field)
Returns the maximum value of this field can have, given the present date.
|7|| int getActualMinimum (int field)
Returns the minimum value of this field can have, given the present date.
|8|| int getGreatestMinimum (int field)
Returns the largest minimum value for a given field, if changed.
|9|| Date getGregorianChange ()
Gets the date changes according to the Gregorian calendar.
|10|| int getLeastMaximum (int field)
Returns the minimum value for this field if it is changed.
|11|| int getMaximum (int field)
Returns the maximum value for this field.
|12|| Date getTime ()
Determines the current time according to the calendar.
|13|| long getTimeInMillis ()
Gets the current time in the Calendar as a long time.
|14|| TimeZone getTimeZone ()
Returns the time zone.
|15|| int getMinimum (int field)
Returns the minimum value for this field.
|16|| int hashCode ()
Override the hash code.
|17|| boolean isLeapYear (int year)
Determines whether a year is a leap year.
Adding or subtracting (up / down) one unit of time in a given time field without changes in large fields.
|19|| void set (int field, int value)
Sets the time field with the specified value.
|20||Set the values for the year, month, and date field.|
|21||Specifies the values for the year, month, date, hour and minute field.|
|22||Sets the values for the year, month, date, hour, minute and then second field.|
|23|| void setGregorianChange (Date date)
Sets the date of the Gregorian calendar modify (change).
|24|| void setTime (Date date)
Sets the current time with the specified date according to this calendar.
|25|| void setTimeInMillis (long millis)
Sets the current time from the specified long value according to this calendar.
|26|| void setTimeZone (TimeZone value)
Sets the time zone with the value of the specified time zone.
|27|| String toString ()
Returns the string representation of the calendar.