CODEWITHSUNDEEP
javadatedatetime
Amar Syla
Amar Syla

Reputation: 3653

Determining if time is full or half hour

I am setting up a date instance like this:

Calendar date = Calendar.getInstance();
date.set(2015, 9, 25, 12, 0);

In this case, I know that it's 12:00, a full hour, but I also have cases where I input the date parameters dynamically, so I want to determine if that date is a full or half hour.

E.g., for 12:00 and 12:30 it would return true, while for 12:23 it would return false.

I've tried timeInMillis % 36000000 from another answer, but it didn't work.

Upvotes: 1

Views: 2285

Answers (3)

Basil Bourque
Basil Bourque

Reputation: 338835

java.time

You can let Java do the work for you. Use the java.time framework to query the date-time value for the minutes, seconds, and fraction-of-second.

ZonedDateTime now = ZonedDateTime.now ( ZoneId.of ( "America/Montreal" ) );
// If the value has any seconds or fraction of a second, we know this is neither full hour nor half hour.
if ( ( now.getSecond () != 0 ) || ( now.getNano () != 0 ) ) {
    System.out.println ( "now: " + now + " is neither full nor half hour, because of seconds or fraction-of-second." );
    return;
}
int minuteOfHour = now.getMinute ();
switch ( minuteOfHour ) {
    case 0:
        System.out.println ( "now: " + now + " is full hour." );
        break;
    case 30:
        System.out.println ( "now: " + now + " is half hour." );
        break;
    default:
        System.out.println ( "now: " + now + " is neither full nor half hour." );
        break;
}

The java.util.Date/.Calendar classes bundled with the early versions of Java are notoriously troublesome, and should be avoided. The java.time framework supplants them.

Upvotes: 0

Shawn D
Shawn D

Reputation: 96

Use get minutes to check the minutes.

int minutes = date.get(Calendar.MINUTE); // gets the minutes
return (minutes == 0 || minutes == 30);

Upvotes: 4

T.J. Crowder
T.J. Crowder

Reputation: 1074555

You're on the right track, you've just used the wrong value. With milliseconds, it would be 1800000. (But see biziclop's comment suggesting that's not a good idea.) I'd get the minutes and use % 30 == 0.

Gratuitous minutes example: (live copy)

for (int n = 0; n < 60; ++n) {
    System.out.println(n + ( n % 30 == 0 ? " <= Yes" : ""));
}

Or in milliseconds: (live copy)

for (int n = 0; n < 3600000; n += 60000) {
    System.out.println(n + ( n % 1800000 == 0 ? " <= Yes" : ""));
}

Upvotes: 2

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