GregorianCalendar and DateFormat Java

Question

I am trying to do a simple exercise where I take a date, add 90 days to it, and format it to something like this:

Monday, April 20, 1998.

I am to do this using GregorianCalendar and DateFormat. So far, I have this compiling code, but I get a runtime error where I cannot format the given Object as Date:

import java.util.*;
import java.text.*;

class Assignment21 {
    public static void main(String args[]) {
        GregorianCalendar ddate = new GregorianCalendar(1994, 10, 20);
        ddate.add(Calendar.DAY_OF_MONTH, 90);
        SimpleDateFormat sdf = new SimpleDateFormat("EEE, MM dd, yyyy");
        String date = sdf.format(ddate);
    }
}

How can I correctly output the predefined GregorianCalendar date using DateFormat?

Answer 1

You have to correct your code:

instead of

String date = sdf.format(ddate);

try:

String date = sdf.format(ddate.getTime());

Answer 2

tl;dr

LocalDate.of( 1994 , Month.OCTOBER , 20 )                  // Generate a date-only value, a `LocalDate` object, without time-of-day and without time zone.
.plusDays( 90 )                                            // Add a span of time. Using immutable objects, a new `LocalDate` object is instantiated, without altering the first.
.format(                                                   
    DateTimeFormatter.ofLocalizedDate( FormatStyle.FULL )
                     .withLocale( Locale.US )
)

Wednesday, January 18, 1995

java.time

You are using troublesome old date-time classes that are now legacy, supplanted by the java.time classes.

LocalDate ld = LocalDate.of( 1994 , 10 , 20 ) ; // Sane numbering for year and month, unlike legacy classes. '1994' = 1994, and 10 = October.
LocalDate ldLater = ld.plusDays( 90 ) ;

Or use Month enum.

LocalDate ld = LocalDate.of( 1994 , Month.OCTOBER , 20 ) ; 
LocalDate ldLater = ld.plusDays( 90 ) ;

Let java.time automatically localize for you.

DateTimeFormatter f = DateTimeFormatter.ofLocalizedDate( FormatStyle.FULL ).withLocale( Locale.US ) ;
String output = ldLater.format( f ) ;

---

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.

You may exchange java.time objects directly with your database. Use a JDBC driver compliant with JDBC 4.2 or later. No need for strings, no need for java.sql.* classes.

Where to obtain the java.time classes?

• Java SE 8, Java SE 9, Java SE 10, 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 (<26), 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.