Using GregorianCalendar with SimpleDateFormat

Question

So, I\'ve been racking my brain over this (should-be) simple exercise to make the program turn a date string into a GregorianCalendar object, format it, and ret

Answer 1

tl;dr

LocalDate.parse(
    "23-Mar-2017" ,
    DateTimeFormatter.ofPattern( "dd-MMM-uuuu" , Locale.US ) 
)

Avoid legacy date-time classes

The Question and other Answers are now outdated, using troublesome old date-time classes that are now legacy, supplanted by the java.time classes.

Using java.time

You seem to be dealing with date-only values. So do not use a date-time class. Instead use LocalDate. The LocalDate class represents a date-only value without time-of-day and without time zone.

Specify a Locale to determine (a) the human language for translation of name of day, name of month, and such, and (b) the cultural norms deciding issues of abbreviation, capitalization, punctuation, separators, and such.

Parse a string.

String input = "23-Mar-2017" ;
DateTimeFormatter f = DateTimeFormatter.ofPattern( "dd-MMM-uuuu" , Locale.US ) ;
LocalDate ld = LocalDate.parse( input , f );

Generate a string.

String output = ld.format( f );

If you were given numbers rather than text for the year, month, and day-of-month, use LocalDate.of.

LocalDate ld = LocalDate.of( 2017 , 3 , 23 );  // ( year , month 1-12 , day-of-month )

See this code run live at IdeOne.com.

input: 23-Mar-2017

ld.toString(): 2017-03-23

output: 23-Mar-2017

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About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.

The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.

To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.

Using a JDBC driver compliant with JDBC 4.2 or later, you may exchange java.time objects directly with your database. No need for strings nor java.sql.* classes.

Where to obtain the java.time classes?

• Java SE 8, Java SE 9, and later
  • Built-in.
  • Part of the standard Java API with a bundled implementation.
  • Java 9 adds some minor features and fixes.
• Java SE 6 and Java SE 7
  • Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
• Android
  • Later versions of Android bundle implementations of the java.time classes.
  • For earlier Android, the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). See How to use ThreeTenABP….

The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, and more.