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In this post, we study how to handle time with java.time.LocalDateTime, java.time.LocalDate and java.time.LocalTime. They are immutable, we use static methods of() to create new objects. Let's study by examples.
OCAJP>cat test.java
import java.time.*;
class test {
public static void main(String... args) {
/*2016-03-13
23:15:27.195
2016-03-13T23:15:27.195
*/
System.out.println("now()");
System.out.println(LocalDate.now()); //yyyy-MM-dd
System.out.println(LocalTime.now()); //HH:mm:ss.sss
System.out.println(LocalDateTime.now()); //yyyy-mm-ddTHH:mm:ss.sss
System.out.println("of()");
System.out.println(LocalDate.of(2016, 1, 1)); //year, month, day
//System.out.println(LocalDate.of(2016, 1, 1000)); //compile, but throw runtime exception
//System.out.println(LocalDate.of(2016, 1, 1000)); //compile, but throw runtime exception
System.out.println(LocalTime.of(1,1,1)); //24 hour, minutes, seconds, no timezone
System.out.println(LocalDateTime.of(2016,1,1,1,1,1)); //date + time, no timezone
/*
Month.JANUARY, Month.FEBERARY, Month.MARCH, Month.APRAIL, etc.
Note Month.JANUARY is 1, while Calendar.JANUARY is 0.
Note Month.JANUARY is 1, while Calendar.JANUARY is 0.
*/
System.out.println("Month enum");
LocalDate d = LocalDate.of(2016, Month.JANUARY, 1);
LocalTime t = LocalTime.of(23, 10, 10, 999); //nanosecond
//LocalDateTime dt = LocalDateTime(d,t); //not compile
LocalDateTime dt = LocalDateTime.of(d,t);
System.out.println(dt);
System.out.println("plusxxx() minusxxx()");
System.out.println(LocalDate.of(2016, 1, 1).plusYears(1).plusMonths(1).plusDays(1));
System.out.println(LocalDate.of(2016, 1, 1).minusYears(1).minusMonths(1).minusDays(1).minusWeeks(1));
System.out.println(LocalTime.of(1,1,1).plusHours(1).plusMinutes(1).plusSeconds(1));
System.out.println(LocalTime.of(1,1,1).minusHours(1).minusMinutes(1).minusSeconds(1).plusNanos(1));
System.out.println(LocalTime.of(1,1,1).minusHours(1).minusMinutes(1).minusSeconds(1).minusNanos(1));
System.out.println(LocalDateTime.now().minusYears(3).plusWeeks(3).minusHours(2).plusNanos(100));
//LocalDate.of(2010,1,1).plusHours(1); //not compile
//LocalTime.of(12,1,1).plusYears(1); //not compile
}
}
OCAJP>javac test.java
OCAJP>java test
now()
2016-03-13
23:46:52.277
2016-03-13T23:46:52.277
of()
2016-01-01
01:01:01
2016-01-01T01:01:01
Month enum
2016-01-01T23:10:10.000000999
plusxxx() minusxxx()
2017-02-02
2014-11-23
02:02:02
00:00:00.000000001
23:59:59.999999999
2013-04-03T21:46:52.278000100
LocalDateTime's plus* and minus* methods are used to add a time period; alternatively, we can use plus(Period p) and minus(Period p) methods, where Period represents a time span.
Lets take a look at examples.
OCAJP>cat test.java
import java.time.*;
class test {
public static void main(String... args) {
Period p = Period.ofYears(3); //static ofYear() is a static method
//LocalDateTime dt = new LocalDateTime.now(); //not compile
LocalDateTime dt = LocalDateTime.now();
System.out.println(dt);
System.out.println(dt.plus(p)); //plus returns a reference of LocalDateTime
p = Period.ofDays(2);
System.out.println(dt.minus(p));
System.out.println(dt); //dt never changed value
System.out.println(dt.plus(Period.ofYears(100).ofDays(1))); //Period is static method, only the last call takes effect
//Period.ofHours(10); //not compile
p = Period.of(1, 1, 1);
System.out.println(dt.plus(p)); //Peroid is 1 year, 1 month, 1 day
}
}
OCAJP>javac test.java
OCAJP>java test
2016-03-14T00:28:04.261
2019-03-14T00:28:04.261
2016-03-12T00:28:04.261
2016-03-14T00:28:04.261
2016-03-15T00:28:04.261
2017-04-15T00:28:04.261
Finally, let's study java.time.format.DateTimeFormater
In order to print out a LocalDate, LocalDateTime, LocalTime in a certain format, we have several ways of doing that.
OCAJP>cat test.java
import java.time.*;
import java.time.format.*;
class test {
public static void main(String... args) {
LocalDate date = LocalDate.of(2016, 1, 1);
System.out.println(date.format(DateTimeFormatter.ISO_LOCAL_DATE));
LocalTime time = LocalTime.of(10, 1, 1);
//standard format
System.out.println(time.format(DateTimeFormatter.ISO_LOCAL_TIME));
LocalDateTime datetime = LocalDateTime.of(date,time);
System.out.println(datetime.format(DateTimeFormatter.ISO_LOCAL_DATE_TIME));
//ofLocalized* format
DateTimeFormatter formater = DateTimeFormatter.ofLocalizedDate(FormatStyle.SHORT);
System.out.println(datetime.format(formater));
//System.out.println(date.format(DateTimeFormatter.ofLocalizedDate())); //required: FormatStyle
//System.out.println(date.format(DateTimeFormatter.ofLocalizedTime(FormatStyle.MEDIUM))); //java.time.temporal.UnsupportedTemporalTypeException
System.out.println(datetime.format(DateTimeFormatter.ofLocalizedTime(FormatStyle.MEDIUM)));
System.out.println(time.format(DateTimeFormatter.ofLocalizedTime(FormatStyle.MEDIUM)));
//ofPattern free format
System.out.println(datetime.format(DateTimeFormatter.ofPattern("MMM dd yyyy, HH mm ss")));
//System.out.println(date.format(DateTimeFormatter.ofPattern("MMMM ddd yy"))); //java.lang.IllegalArgumentException: Too many pattern letters: d
System.out.println(date.format(DateTimeFormatter.ofPattern("MMMM dd yy")));
//System.out.println(time.format(DateTimeFormatter.ofPattern("M d yy, hh:mm:ss"))); //java.time.temporal.UnsupportedTemporalTypeException: Unsupported field: MonthOfYear
System.out.println(time.format(DateTimeFormatter.ofPattern("hh:mm:ss")));
//format() method can also be invoked on formatter
System.out.println(DateTimeFormatter.ISO_LOCAL_DATE.format(date));
System.out.println(DateTimeFormatter.ofLocalizedTime(FormatStyle.SHORT).format(time));
System.out.println(DateTimeFormatter.ofPattern("yyyy MMM dd HH:mm:ss").format(datetime));
}
}
OCAJP>javac test.java
OCAJP>java test
2016-01-01
10:01:01
2016-01-01T10:01:01
1/1/16
10:01:01 AM
10:01:01 AM
Jan 01 2016, 10 01 01
January 01 16
10:01:01
2016-01-01
10:01 AM
2016 Jan 01 10:01:01
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