The class LocalDateTime is a combination of LocalDate and LocalTime that keeps such values as 2017-12-03T22:30. It still doesn’t store information on a time-zone. It could be used to store a date and time of a transaction in a payment system. As in the LocalTime class, time is represented to nanosecond precision.

Creating LocalDateTime and current time

An instance of LocalDateTime that represents this current moment can be obtained as below:

LocalDateTime now = LocalDateTime.now(); // this moment

The class has static methods of and parse to create instances:

LocalDateTime dt1 = LocalDateTime.of(2017, 11, 25, 22, 30);  // 25 November 2017, 22:30
LocalDateTime dt2 = LocalDateTime.parse("2017-11-25T22:30"); // 25 November 2017, 22:30

It’s also possible to obtain an instance from the instances of LocalDate and LocalTime, like this:

LocalDate date = LocalDate.of(2017, 11, 25); // 2017-11-25
LocalTime time = LocalTime.of(21, 30); // 21:30
        
LocalDateTime dateTime = LocalDateTime.of(date, time); // 2017-11-25T21:30

or by using special instance methods of LocalDate and LocalTime:

LocalDate date = LocalDate.of(2017, 11, 25); // 2017-11-25
LocalTime time = LocalTime.of(21, 30); // 21:30       

LocalDateTime dateTime1 = date.atTime(time); // 2017-11-25T21:30
LocalDateTime dateTime2 = time.atDate(date); // 2017-11-25T21:30

LocalDateTime: from years to minutes

Now let’s observe some methods of the LocalDateTime class. We’ve already created an instance dateTime to represent the 25 of November, 2017, 10:30 pm :

LocalDateTime dateTime = LocalDateTime.of(2017, 11, 25, 22, 30); // 25 November 2017, 22:30

The class LocalDateTime has methods for obtaining units of date and time, such as a month, day of the month, hour and minute:

int month = dateTime.getMonthValue(); // 11
int day = dateTime.getDayOfMonth(); // 25
int hour = dateTime.getHour(); // 22
int minute = dateTime.getMinute(); // 30

The class also has instance methods toLocalDate and toLocalTime to get the date and time as the whole parts of LocalDateTime:

LocalDate dateOf = dateTime.toLocalDate(); // 2017-11-25
LocalTime timeOf = dateTime.toLocalTime(); // 22:30

Arithmetic methods of LocalDateTime

The class has methods to add, subtract and alter years, months, days, hours, minutes, seconds as well as LocalDate and LocalTime. Let’s explore them with a different example:

LocalDateTime endOf2017 = LocalDateTime.of(2017, 12, 31, 23, 59, 59); // 2017-12-31T23:59:59

This is how by adding one second we get into another year or move by years:

LocalDateTime beginningOf2018 = endOf2017.plusSeconds(1); // 2018-01-01T00:00
LocalDateTime beginningOf2020 = beginningOf2018.plusYears(2); // 2020-01-01T00:00

We can also alter the constituents of the LocalDateTime by indicating its values:

LocalDateTime beginningOf2020 = beginningOf2018.withYear(2020); // 2020-01-01T00:00

As you see, LocalDateTime is another immutable class from the java.time package. It represents a combination of LocalDate and LocalTime.

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