1. Java Date Time Tutorial
2. Java System.currentTimeMillis()
3. Java Time Measurement
4. Java's java.util.Date
5. Java's java.sql.Date
6. Java's java.sql.Timestamp
7. Java's java.util.Calendar and GregorianCalendar
8. Java's java.util.TimeZone
9. Parsing and Formatting Dates in Java
10. Java Instant
11. Java Duration
12. Java LocalDate
13. Java LocalTime
14. Java LocalDateTime
15. Java ZonedDateTime
16. Java DateTimeFormatter

• Creating a LocalDateTime
• Accessing the Time of a LocalDateTime
• Date Time Calculations

The LocalDateTime class in the Java 8 date time API (java.time.LocalDateTime) represents a local date and time without any time zone information. You could view the LocalDateTime as a combination of the LocalDate and LocalTime classes of the Java 8 date time API.

The LocalDateTime is immutable, so all methods that perform calculations on the LocalDateTime return a new LocalDateTime instance.

Creating a LocalDateTime

You create a LocalDateTime object via one of its static factory methods. Here is an example that shows how to create a LocalDateTime object via the now() method:

LocalDateTime localDateTime = LocalDateTime.now();

Another way to create a LocalDateTime object is to create it based on a specific year, month, day etc. Here is an example of that:

LocalDateTime localDateTime2 =
    LocalDateTime.of(2015, 11, 26, 13, 55, 36, 123);

The parameters to the of() method are year, month, day (of month), hours, minutes, seconds and nanoseconds.

Accessing the Time of a LocalDateTime

You can access the date and time fields of the LocalDateTime using some of these methods:

• getYear()
• getMonth()
• getDayOfMonth()
• getDayOfWeek()
• getDayOfYear()
• getHour()
• getMinute()
• getSecond()
• getNano()

Some of these methods return an int and some of them return an enum. Via the methods that return an enum you can get an int representation of the enum by calling the getValue() of the enum .

Date Time Calculations

You can perform various date time calculations on the LocalDateTime object using some of these methods:

• plusYears()
• plusMonths()
• plusDays()
• plusHours()
• plusMinutes()
• plusSeconds()
• plusNanos()
• minusYears()
• minusMonths()
• minusDays()
• minusHours()
• minusMinutes()
• minusSeconds()
• minusNanos()

Here are a few examples to illustrate how these calculation methods work:

LocalDateTime localDateTime  = LocalDateTime.now();

LocalDateTime localDateTime1 = localDateTime.plusYears(3);
LocalDateTime localDateTime2 = localDateTime.minusYears(3);

The first line creates a LocalDateTime instance representing the moment of now. The second line creates a LocalDateTime object that represents a date and time 3 years later. The third line creates a LocalDateTime object that represents a date and time 3 years earlier.