CODEWITHSUNDEEP
javadatecalendar
Marc Rasmussen
Marc Rasmussen

Reputation: 20555

Check if the Calendar date is a sunday

I am trying to figure out how to make my program count the number of Sundays in a week.

I have tried the following thing:

if (date.DAY_OF_WEEK == date.SUNDAY) {
    System.out.println("Sunday!");
}

Yet it does not seem to work?

When I try to System.out.Println the date.DAY_OF_WEEK I get: 7

Does anyone know how I can check if the current calendar date is Sunday?

UPDATE FOR MORE INFORMATION

  1. firt of all the date.DAY_OF_WEEK is a Calendar object!

  2. i made sure to set the Calendar object date to a sunday

The system out print where i get 7 is what it returns to me when i try to run date.DAY_OF_MONTH even if the day it set to a sunday

2nd UPDATE TO ALEX

This is more or less my code

Calendar startDate = Calendar.getInstance();

    startDate.set(2012, 12, 02);
    if (startDate.get(Calendar.DAY_OF_WEEK) == Calendar.SUNDAY) {
        System.out.println("true");
    }else {
        System.out.println("FALSE");
    }

Upvotes: 12

Views: 44926

Answers (3)

Basil Bourque
Basil Bourque

Reputation: 338276

tl;dr

boolean todayIsSunday = LocalDate.now( ZoneId.of( "America/Montreal" ) ).getDayOfWeek().equals( DayOfWeek.SUNDAY ) ;

java.time

The other Answers are outdated. The modern approach uses java.time classes.

LocalDate

The LocalDate class represents a date-only value without time-of-day and without time zone or offset-from-UTC.

A time zone is crucial in determining a date. For any given moment, the date varies around the globe by zone. For example, a few minutes after midnight in Paris France is a new day while still “yesterday” in Montréal Québec.

If no time zone is specified, the JVM implicitly applies its current default time zone. That default may change at any moment during runtime(!), so your results may vary. Better to specify your desired/expected time zone explicitly as an argument. If critical, confirm the zone with your user.

Specify a proper time zone name in the format of Continent/Region, such as America/Montreal, Africa/Casablanca, or Pacific/Auckland. Never use the 2-4 letter abbreviation such as EST or IST as they are not true time zones, not standardized, and not even unique(!).

ZoneId z = ZoneId.of( "America/Montreal" ) ;  
LocalDate today = LocalDate.now( z ) ;

If you want to use the JVM’s current default time zone, ask for it and pass as an argument. If omitted, the code becomes ambiguous to read in that we do not know for certain if you intended to use the default or if you, like so many programmers, were unaware of the issue.

ZoneId z = ZoneId.systemDefault() ;  // Get JVM’s current default time zone.

Or specify a date. You may set the month by a number, with sane numbering 1-12 for January-December.

LocalDate ld = LocalDate.of( 1986 , 2 , 23 ) ;  // Years use sane direct numbering (1986 means year 1986). Months use sane numbering, 1-12 for January-December.

Or, better, use the Month enum objects pre-defined, one for each month of the year. Tip: Use these Month objects throughout your codebase rather than a mere integer number to make your code more self-documenting, ensure valid values, and provide type-safety. Ditto for Year & YearMonth.

LocalDate ld = LocalDate.of( 1986 , Month.FEBRUARY , 23 ) ;

DayOfWeek

For any LocalDate, you can obtain its day-of-week as a DayOfWeek object. The DayOfWeek enum automatically instantiates seven objects, one for each day of the week.

boolean isSunday = ld.getDayOfWeek().equals( DayOfWeek.SUNDAY ) ;

One Sunday per week

count the number of Sundays in a week.

That would be 1, always one Sunday per week.

If your goal is finding the next Sunday, use a TemporalAdjuster defined in TemporalAdjusters class.

TemporalAdjuster ta = TemporalAdjusters.nextOrSame( DayOfWeek.SUNDAY ) ;
LocalDate nextOrSameSunday = ld.with( ta ) ;

Table of date-time types in Java, both modern and legacy

About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.

To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.

The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.

You may exchange java.time objects directly with your database. Use a JDBC driver compliant with JDBC 4.2 or later. No need for strings, no need for java.sql.* classes. Hibernate 5 & JPA 2.2 support java.time.

Where to obtain the java.time classes?

Upvotes: 3

Modus Tollens
Modus Tollens

Reputation: 5123

Note: the Joda-Time project is now in maintenance mode. See this answer if you don't have to work with legacy code.

If you have to work with date or time a lot, you might want to try using Joda-Time.

Your code would look something like this:

LocalDate startDate = new LocalDate(2012, 12, 2);
int day = startDate.dayOfWeek().get();   // gets the day of the week as integer

if (DateTimeConstants.SUNDAY == day) {
    System.out.println("It's a Sunday!");
}

You can also get a text string from dayOfWeek():

String dayText = startDate.dayOfWeek().getAsText();

will return the string "Sunday".

Upvotes: 3

Alex
Alex

Reputation: 25613

Calendar cal = ...;
if (cal.get(Calendar.DAY_OF_WEEK) == Calendar.SUNDAY) {
    System.out.println("Sunday!");
}

Calendar.DAY_OF_WEEK always equals to 7 no matter what instance of Calendar you are using (see this link), it is a constant created to be used with the Calendar.get() method to retrieve the correct value.

It is the call to Calendar.get(Calendar.DAY_OF_WEEK) that will return the real day of week. Besides, you will find useful values in the Calendar class like Calendar.SUNDAY (and the other days and months) in order for you to be more explicit in your code and avoid errors like JANUARY being equal to 0.

Edit

Like I said, the Calendar class does contains useful constants for you to use. There is no month number 12 they start at 0 (see above), so DECEMBER is month number 11 in the Java Date handling.

Calendar startDate = Calendar.getInstance();
startDate.set(2012, Calendar.DECEMBER, 02);
if (startDate.get(Calendar.DAY_OF_WEEK) == Calendar.SUNDAY) {
    System.out.println("true");
} else {
    System.out.println("FALSE");
}

Will print true of course.

Upvotes: 33

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