Java8の日時APIはとりあえずこれだけ覚えとけ ref: http://qiita.com/tag1216/items/91a471b33f383981bfaa

file0.java

LocalDateTime d = LocalDateTime.now();

file1.java

//年月日時分秒を指定
LocalDateTime d1 = LocalDateTime.of(2015, 12, 15, 23, 30, 59);
//年月日時分秒と1秒未満のナノ秒を指定
LocalDateTime d2 = LocalDateTime.of(2015, 12, 15, 23, 30, 59, 999999999);

file10.java

//Date -> *DateTime
Date date = new Date();
ZonedDateTime zdt = date.toInstant().atZone(ZoneId.systemDefault());
LocalDateTime ldt = LocalDateTime.ofInstant(date.toInstant(), ZoneId.systemDefault());
OffsetDateTime odt = OffsetDateTime.ofInstant(date.toInstant(), ZoneId.systemDefault());

//ZonedDateTime -> Date
ZonedDateTime zdt = ZonedDateTime.now();
Date date = Date.from(zdt.toInstant());

//OffsetDateTime -> Date
OffsetDateTime odt = OffsetDateTime.now();
Date date = Date.from(odt.toInstant());

//LocalDateTime -> Date
LocalDateTime ldt = LocalDateTime.now();
Date date = Date.from(ldt.atZone(ZoneId.systemDefault()).toInstant());

file2.java

LocalDateTime d = LocalDateTime.now();
System.out.println(d.getYear());
System.out.println(d.getMonth());
System.out.println(d.getDayOfMonth());
System.out.println(d.getHour());
System.out.println(d.getMinute());
System.out.println(d.getSecond());
System.out.println(d.getNano());
System.out.println(d.get(ChronoField.YEAR));

file3.java

LocalDateTime d = LocalDateTime.of(2015, 12, 15, 23, 30, 59);
System.out.println(d.plusDays(20));       //2016-01-04T23:30:59
System.out.println(d.minusDays(20));      //2015-11-25T23:30:59
System.out.println(d.withDayOfMonth(20)); //2015-12-20T23:30:59

file4.java

LocalDateTime.of(2015, 12, 15, 23, 30, 59).truncatedTo(ChronoUnit.HOURS);
// 2015-12-15T23:00

file5.java

LocalDateTime d = 
        LocalDateTime.now()
        .plusMonths(1)
        .withDayOfMonth(1)
        .withHour(12)
        .truncatedTo(ChronoUnit.HOURS);

file6.java

ZoneId zoneId = ZoneId.systemDefault();
ZoneId zoneId = ZoneId.of("Asia/Tokyo");
ZoneOffset offset = ZoneOffset.UTC;
ZoneOffset offset = ZoneOffset.ofHours(9);
ZoneOffset offset = ZoneId.systemDefault().getRules().getOffset(Instant.now());

file7.java

LocalDateTime ldt = LocalDateTime.now();
//LocalDateTime -> ZoneDateTime
ZonedDateTime zdt = ldt.atZone(ZoneId.systemDefault());
//LocalDateTime -> OffsetDateTime
OffsetDateTime odt = ldt.atOffset(ZoneOffset.ofHours(9));
//LocalDateTime -> Instant
Instant instant = ldt.toInstant(ZoneOffset.UTC);

file8.java

LocalDateTime.parse("2015-12-15T23:30");
LocalDateTime.parse("2015-12-15T23:30:59");
LocalDateTime.parse("2015-12-15T23:30:59.999");

file9.java

DateTimeFormatter f = DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss");
LocalDateTime d = LocalDateTime.parse("2015/12/15 23:30:59", f);
System.out.println(d.format(f));