Date and Time

Date and Time
Use different libraries for differnt needs
- LocalDate for just the date
- LocalTime for just the time
- LocalDateTime for both time and date
- ZoneDateTime for time, date and time zone

LocalDate

Examples:

The date to day is 13 May 2018

NOTE the return values is just the toString() representation of LocalDate.

Getting current date, in format YYYY-MM-DD

LocalDate dateNow = LocalDate.now();
//return 2018-05-13

Can do some maths with the date

dateNow.plusDays(3);
// return 2018-05-16

dateNow.minus(5, ChronoUnit.MONTHS);
// returns 2017-12-13

There are lots of methods to use

Can do some comparisions

boolean equal = dateNow.isEqual(dateNow);
// returns true

dateNow.isBefore(dateNow.minusDays(1));
// reutrns false

Formatting the date

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("d/MM/uuuu");
String formattedDate = dateNow.format(formatter);
//returns 13/05/2018

Parsing string date

LocalDate parseDate = LocalDate.parse("2016-08-16");

LocalDate parsedDateFormatted = LocalDate.parse("16-Aug-2016", DateTimeFormatter.ofPattern("d-MMM-yyyy"));

LocalDate parsedDateWordFormatted = LocalDate.parse("Tue, Aug 16 2016", DateTimeFormatter.ofPattern("E, MMM d yyyy"));

Note the pattern of formatter matches the string representation of the date, and thus can turn into LocalDate format
list of patterns
- https://docs.oracle.com/javase/8/docs/api/java/time/format/DateTimeFormatter.html

Creating Date

LocalDate someDate = LocalDate.of(2015, Month.JANUARY, 20);
//returns 2015-01-20

LocalDate someOtherDate = LocalDate.of(2016, 11, 19);
// return 2016-11-19

Get parts of the date

dateNow.get(ChronoField.MONTH_OF_YEAR);
// returns 5 (May is 5th month of year)

DayOfWeek dayOfWeek = dateNow.getDayOfWeek();
// return sunday

Alter parts of the date

LocalDate changedDayOfWeek = dateNow.withDayOfMonth(DayOfWeek.FRIDAY.getValue());
// return 2018-05-05

LocalDate dateWithChangedYear = dateNow.with(ChronoField.YEAR, 2024);
// returns 2024-05-13

LocalTime

Very similar methods to those in LocalDate

LocalDateTime

Very similar methods to those in LocalDate

ZoneDateTime

Duration

https://docs.oracle.com/javase/8/docs/api/java/time/Duration.html

Time measurement

A great way of measuring how long a method call takes.

long startTime = System.currentTimeMillis();

someMethodToMeasure();

long endTime   = System.currentTimeMillis();

long totalTime = endTime - startTime;

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Last updated 5 years ago

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