How to print a date with or without offset?

PrintingDateWithOffset.java

import java.util.Locale;

import net.time4j.PlainDate;
import net.time4j.format.expert.ChronoFormatter;
import net.time4j.format.expert.PatternType;
import net.time4j.tz.OffsetSign;
import net.time4j.tz.ZonalOffset;


/**
 * Demonstrates how to print plain calendar dates with timezone offset.
 * 
 * Following examples use optional format sections.
 * 
 * Without any special action, optional format sections are only optional
 * during parsing, but not during printing. However, to specifiy an optional
 * printing section, users can specify a special printing condition
 * telling Time4J when to suppress printing.
 */
public class PrintingDateWithOffset {
  
  public static void main(String... args) {
    
	// first example: date without offset, the formatter throws the expected exception
	try {
		ChronoFormatter<PlainDate> f1 =
		  ChronoFormatter.ofDatePattern("uuuuMMdd[XX]", PatternType.CLDR, Locale.ROOT);
		f1.format(PlainDate.of(2016, 7, 20));
	} catch (IllegalArgumentException iae) {
		System.out.println(iae.getMessage()); // Cannot extract timezone offset from format attributes for: 2016-07-20
	}
	
	// second example: remember that a calendar date has no offset, hence the offset must be explicitly specified
  	ChronoFormatter<PlainDate> f2 =
  		ChronoFormatter.ofDatePattern("uuuuMMdd[XX]", PatternType.CLDR, Locale.ROOT)
  		  .withTimezone(ZonalOffset.ofHoursMinutes(OffsetSign.AHEAD_OF_UTC, 5, 30));
  	System.out.println(f2.format(PlainDate.of(2016, 7, 20))); // 20160720+0530
  	
  	// third example: does not make much sense, just for explaining the usage of an optional printing section
  	// However, such a formatter could be useful if users write a specialized date chronology with optional offset
  	// for modelling XML-type xsd:date
  	ChronoFormatter<PlainDate> f3 =
  		ChronoFormatter.setUp(PlainDate.axis(), Locale.ROOT)
  		  .addPattern("uuuuMMdd", PatternType.CLDR)
  		  .startOptionalSection(d -> d.hasTimezone()) // only printing when date has offset (never true)
  		  .addTimezoneOffset()
  		  .endSection()
  		  .build()
  		  .withTimezone(ZonalOffset.ofHoursMinutes(OffsetSign.AHEAD_OF_UTC, 5, 30) // unused, see print condition above
  		);
  	System.out.println(f3.format(PlainDate.of(2016, 7, 20))); // 20160720
  }
}