旧日時APIとの相互変換＆Java 6／7でDate-Time APIが使えるライブラリThreeTen Backport：ここが大変だよJava 8 Date-Time API（終）（2/3 ページ）

// Date → Instant
System.out.println("Date → Instant");
 
Date date1 = new Date();
Instant instant1 = date1.toInstant();
 
System.out.println("date1=" + date1);
System.out.println("instant1=" + instant1);
System.out.println("date1.getTime()=" + date1.getTime());
System.out.println("instant1.toEpochMilli()=" + instant1.toEpochMilli());
 
// Instant → Date
System.out.println("Instant → Date");
 
Instant instant2 = Instant.now();
Date date2 = Date.from(instant2);
 
System.out.println("instant2=" + instant2);
System.out.println("date2=" + date2);
System.out.println("instant2.toEpochMilli()=" + instant2.toEpochMilli());
System.out.println("date2.getTime()=" + date2.getTime());
 
// Calendar → Instant
System.out.println("Calendar → Instant");
 
Calendar calendar = Calendar.getInstance();
Instant instant3 = calendar.toInstant();
 
System.out.println("calendar=" + calendar);
System.out.println("instant3=" + instant3);
System.out.println("calendar.getTimeInMillis()=" + calendar.getTimeInMillis());
System.out.println("instant3.toEpochMilli()=" + instant3.toEpochMilli());

// GregorianCalendar → ZonedDateTime
System.out.println("GregorianCalendar → ZonedDateTime");
 
GregorianCalendar calendar2 = (GregorianCalendar) GregorianCalendar.getInstance();
ZonedDateTime zonedDateTime = calendar2.toZonedDateTime();
 
System.out.println("calendar2=" + calendar2);
System.out.println("zonedDateTime=" + zonedDateTime);
 
System.out.println();
 
// ZonedDateTime → GregorianCalendar
System.out.println("ZonedDateTime → GregorianCalendar");
 
GregorianCalendar calendar3 = GregorianCalendar.from(zonedDateTime);
 
System.out.println("zonedDateTime=" + zonedDateTime);
System.out.println("calendar3=" + calendar3);

// TimeZone → ZoneId
System.out.println("TimeZone → ZoneId");
 
TimeZone timeZone1 = TimeZone.getTimeZone("America/Los_Angeles");
ZoneId zoneId1 = timeZone1.toZoneId();
 
System.out.println("timeZone1=" + timeZone1);
System.out.println("zoneId1=" + zoneId1);
 
System.out.println();
 
// ZoneId → TimeZone
System.out.println("ZoneId → TimeZone");
 
ZoneId zoneId2 = ZoneId.of("Asia/Tokyo");
TimeZone timeZone2 = TimeZone.getTimeZone(zoneId2);
 
System.out.println("timeZone2=" + timeZone2);
System.out.println("zoneId2=" + zoneId2);
 
System.out.println();
 
// ZoneOffset → TimeZone
System.out.println("ZoneId → TimeZone");
 
ZoneOffset zoneOffset = ZoneOffset.of("+01:00");
TimeZone timeZone4 = TimeZone.getTimeZone(zoneOffset);
 
System.out.println("timeZone4=" + timeZone4);
System.out.println("zoneOffset=" + zoneOffset);

LocalDate localDate = LocalDate.of(2014, 1, 1);
Instant instant = Instant.from(localDate.atStartOfDay(ZoneId.systemDefault()));
Date date = Date.from(instant);
 
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("uuuu/M/d");
Format format = formatter.toFormat();
System.out.println(format);
System.out.println("format.format(localDate)=" + format.format(localDate));
System.out.println("format.format(date)=" + format.format(date)); // 例外が発生する

// DateTimeFormatter → Formatへの変換
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("uuuu/M/d");
Format format = formatter.toFormat();
 
// Formatから文字列の解析
Object parsedObject = format.parseObject("2014/2/2");
System.out.println("parsedObject=" + parsedObject);
System.out.println("parsedObject.getClass()=" + parsedObject.getClass());
 
// Parsed → Date-Time API
TemporalAccessor temporalAccessor = (TemporalAccessor) parsedObject;
LocalDate converted = LocalDate.from(temporalAccessor);
System.out.println("converted=" + converted);
System.out.println("converted.getClass()=" + converted.getClass());
 
// TemporalQueryを使って直接Date-Time APIのクラスに変換
Format format2 = formatter.toFormat(LocalDate::from);
Object parsedObject2 = format2.parseObject("2014/3/3");
System.out.println("parsedObject2=" + parsedObject2);
System.out.println("parsedObject2.getClass()=" + parsedObject2.getClass());