# Date and Time

* [Date and Time](#date-and-time)
  * [LocalDate](#localdate)
  * [LocalTime](#localtime)
  * [LocalDateTime](#localdatetime)
    * [Links](#links)
  * [ZoneDateTime](#zonedatetime)
  * [Duration](#duration)
  * [Time measurement](#time-measurement)
  * [links](#links)
* 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

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

Can do some maths with the date

```java
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

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

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

Formatting the date

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

Parsing string date

```java
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

```java
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

```java
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

```java
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

```java
```

### Links

## 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.

```java
long startTime = System.currentTimeMillis();

someMethodToMeasure();

long endTime   = System.currentTimeMillis();

long totalTime = endTime - startTime;
```

* <http://tutorials.jenkov.com/java-date-time/time-measurement.html>

  **links**
* <https://dzone.com/articles/java-8-date-and-time>
* <http://www.oracle.com/technetwork/articles/java/jf14-date-time-2125367.html>
* <http://www.baeldung.com/java-8-date-time-intro>
* <https://www.tutorialspoint.com/java8/java8_datetime_api.htm>
* <https://www.journaldev.com/2800/java-8-date-localdate-localdatetime-instant>
* <http://tutorials.jenkov.com/java-date-time/index.html>
* <https://github.com/winterbe/java8-tutorial#date-api>