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What's New in Java 8 - Date API

With the final release of Java 8 around the corner, one of the new features I’m excited about is the new Date API, a result of the work on JSR 310. While Lambda expressions are certainly the big draw of Java 8, having a better way to work with dates is a decidedly welcome addition. This is a quick post (part 1 of 2 or 3) showing some highlights of the new Date functionality, this time mostly around the LocalDate class.

Creating New Date Objects

Creating a new Date object representing a specific day is as easy as:

LocalDate today = LocalDate.parse("2014-02-27");
//or this method
LocalDate bday = LocalDate.of(2014,3,18);

Adding To Dates

As an example of the ease with which we can work with dates in Java 8, consider the case where we need to add either days, months or years to an existing date. There are the methods LocalDate.plusDays,LocalDate.plusWeeks, LocalDate.plusMonths LocalDate.plusYears. There is also a generic LocalDate.plus method where you specify how much to add and the time unit via a TemporalUnit type. Here some examples:

    @Test
    public void test_add_to_date() {

        LocalDate oneMonthFromNow = today.plusDays(30);
        assertTrue(oneMonthFromNow.isEqual(LocalDate.parse("2014-03-29")));

        LocalDate nextMonth = today.plusMonths(1);
        assertTrue(nextMonth.isEqual(LocalDate.parse("2014-03-27")));

        LocalDate future = today.plus(4, ChronoUnit.WEEKS);
        assertTrue(future.isEqual(LocalDate.parse("2014-03-27")));

    }

Subtracting From Dates

To subtract days, weeks, months or years from a date there the expected methods: LocalDate.minusDays, LocalDate.minusMonths etc. Here’s some examples of subtracting from a date:

   @Test
    public void test_subtract_from_date() {

        assertThat(today.minusWeeks(1).toString(), is("2014-02-20"));

        assertThat(today.minusMonths(2).toString(), is("2013-12-27"));

        assertThat(today.minusYears(4).toString(), is("2010-02-27"));

        Period twoMonths = Period.ofMonths(2);

        assertThat(today.minus(twoMonths).toString(), is("2013-12-27"));

    }

In this example we also introduced the Period object.

Determining Difference Between Dates

It could be argued getting the difference between two dates was the most painful operation to do with dates prior to Java 8. The new Date API makes determining the amount of days,weeks,months or years between dates equally as easy with the LocalDate.until method:

@Test
    public void test_get_days_between_dates() {
        LocalDate vacationStart = LocalDate.parse("2014-07-04");
        Period timeUntilVacation = today.until(vacationStart);

        assertThat(timeUntilVacation.getMonths(), is(4));

        assertThat(timeUntilVacation.getDays(), is(7));

        assertThat(today.until(vacationStart, ChronoUnit.DAYS), is(127L));

        LocalDate libraryBookDue = LocalDate.parse("2000-03-18");

        assertThat(today.until(libraryBookDue).isNegative(), is(true));


        assertThat(today.until(libraryBookDue, ChronoUnit.DAYS), is(-5094L));

        LocalDate christmas = LocalDate.parse("2014-12-25");
        assertThat(today.until(christmas, ChronoUnit.DAYS), is(301L));

    }

In this example we see the use of the Period object again.

Conclusion

We’ve wrapped up our quick tour of the LocalDate and the Java 8 Date API. Obviously, there is so much more to discover about working with dates and time in Java 8, this post is just a quick introduction. Thanks for your time.

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