I am trying to parse "Mon 00:00-23:59" using LocalTime.

LocalTime start = LocalTime.parse("00:00", DateTimeFormatter.ofPattern("HH:mm"));
LocalTime end = LocalTime.parse("23:59", DateTimeFormatter.ofPattern("HH:mm"));

But, start.isBefore(end) returns true, how is this possible?

I need to know if the start time is later than or equal to the end time.

CodePudding user response：

Your issue has nothing to do with parsing.

And, the behavior you see is a feature, not a bug.

LocalTime represent the time of day for a single imaginary generic 24-hours-long day. That day starts at 00:00:00.0. So all other values are after that zero time value.

So this should return true:

LocalTime.parse( "00:00" ).isBefore( LocalTime.parse( "23:59" ) )  // true.

Be aware that in our politically-defined timekeeping systems days are not necessarily 24-hours long, nor do they necessarily start at 00:00. Some days may be 23, 23.5, 25, or other number of hours long. And some dates in some time zones may start at a time such as 01:00.

By the way, notice there is no need to specify a DateTimeFormatter when the input complies with ISO 8601 standard for date-time textual values.

CodePudding user response：

Note that

• The modern Date-Time API is based on ISO 8601 and does not require using a DateTimeFormatter object explicitly as long as the Date-Time string conforms to the ISO 8601 standards. Your time strings are in ISO 8601 format.
• The local time, 00:00 corresponds to 12:00 AM whereas 23:59 corresponds to 11:59 PM, it's obvious that 00:00 is before 23:59. So, the results that you have got is correct.

To avoid confusion, I recommend you attach a date with the local time i.e. use LocalDateTime.

Demo:

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.format.DateTimeFormatter;
import java.util.Locale;

public class Main {
    public static void main(String[] args) {
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("hh:mm a", Locale.ENGLISH);

        LocalTime start = LocalTime.parse("00:00");
        LocalTime end = LocalTime.parse("23:59");

        System.out.println(start.format(dtf));
        System.out.println(end.format(dtf));

        LocalDate today = LocalDate.now();

        LocalDateTime ldtStart = start.atDate(today);
        LocalDateTime ldtEnd = end.atDate(today);
        System.out.println(ldtStart);
        System.out.println(ldtEnd);

        // Notice the result when you add a minute to ldtEnd
        System.out.println(ldtEnd.plusMinutes(1));
    }
}

Output:

12:00 AM
11:59 PM
2021-10-30T00:00
2021-10-30T23:59
2021-10-31T00:00

ONLINE DEMO

Learn more about the modern Date-Time API^* from Trail: Date Time.

^{* If you are working for an Android project and your Android API level is still not compliant with Java-8, check Java 8 APIs available through desugaring. Note that Android 8.0 Oreo already provides support for java.time.}