Joda time: DateTimeComparator. What is similar in Java 8 Time Api?
With Joda Time, you are able to do a really cool things, for example:
package temp;
import org.joda.time.DateTime;
import org.joda.time.DateTimeComparator;
import org.joda.time.DateTimeFieldType;
public class TestDateTimeComparator {
public static void main(String[] args) {
//Two DateTime instances which have same month, date, and hour
//but different year, minutes and seconds
DateTime d1 = new DateTime(2001,05,12,7,0,0);
DateTime d2 = new DateTime(2014,05,12,7,30,45);
//Define the lower limit to be hour and upper limit to be month
DateTimeFieldType lowerLimit = DateTimeFieldType.hourOfDay();
DateTimeFieldType upperLimit = DateTimeFieldType.monthOfYear();
//Because of the upper and lower limits , the comparator shall only consider only those sub-elements
//within the lower and upper limits i.e.month, day and hour
//It shall ignore those sub-elements outside the lower and upper limits: i.e year, minute and second
DateTimeComparator dateTimeComparator = DateTimeComparator.getInstance(lowerLimit,upperLimit);
int result = dateTimeComparator.compare(d1, d2);
switch (result) {
case -1:
System.out.println("d1 is less than d2");
break;
case 0:
System.out.println("d1 is equal to d2");
break;
case 1:
System.out.println("d1 is greater than d2");
break;
default:
break;
}
}
}
I found this example here.
I want to have the same steps but with Java Time API, but unfortunately, I do not see any similar Comparators.
How can I compare only certain date and time fields but not others with Java Time API?
You can replicate some of this behavior, a bit more manually, with the general-purpose helper methods provided on Comparators .
Assuming that we import static java.util.Comparators.comparing; , we can define a comparator on LocalDateTimes that compares only the month:
Comparator<LocalDateTime> byMonth = comparing(LocalDateTime::getMonth);
or one that compares only the month, day, and hour, as in your example:
Comparator<LocalDateTime> byHourDayMonth = comparing(LocalDateTime::getMonth) //
.thenComparing(LocalDateTime::getDayOfMonth) //
.thenComparing(LocalDateTime::getHour);
This does leave you in the position of manually deciding the order... not quite as automatic but with some more fine-grained control.
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