Not displaying day of the week using calendar and date instances

Question

I have created new SimpleDateFormat object which parses the given string as date object. The date format is as below:

SimpleDateFormat simpledateFormat = new SimpleDateFormat("dd-MM-yyyy");

And I am setting this date to calendar instance as below:

Date date = sampledateFormat.parse("01-08-2013");
Calendar calendar = Calendar.getInstance();
calendar.setTime(date);

Now I am getting the day of the day of the week from this calendar. It is giving wrong value.

System.out.println(calendar.DAY_OF_WEEK);

The output it is giving is 7 i.e. Saturday but the expected value is 5 i.e. Thursday. Whats the problem?

Answer 1

You should print

calendar.get(Calendar.DAY_OF_WEEK);

The Calendar class has DAY_OF_WEEK as integer constant (with value 7) which should be used in conjunction with the Calendar.get(int) method. DAY_OF_WEEK is a calendar field, and all these constant fields are used to get() different values from the calendar instance. Their value is irrelevant.

Answer 2

tl;dr

LocalDate.parse(    // Parse the input string by specified formatting pattern to get a date-only `LocalDate` object.
    "01-08-2013" , 
    DateTimeFormatter.ofPattern( "dd-MM-uuuu" )
)
.getDayOfWeek()    // Get a `DayOfWeek` enum object. This is *not* a mere String.
.getValue()        // Ask the `DayOfWeek` object for its number, 1-7 for Monday-Sunday per ISO 8601 standard.

4

java.time

The modern approach uses the java.time classes that supplanted the troublesome old legacy date-time classes such as SimpleDateFormat and Date and Calendar.

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

Define a formatting pattern to match.

DateTimeFormatter f = DateTimeFormatter.ofPattern( "dd-MM-uuuu" ) ;

Parse the input string.

LocalDate ld = LocalDate.parse( "01-08-2013" , f ) ;

ld.toString(): 2013-08-01

Interrogate for the day-of-week. Get a DayOfWeek enum object, one of seven pre-defined objects, for Monday-Sunday.

DayOfWeek dow = ld.getDayOfWeek() ;

dow.toString(): THURSDAY

You can ask that DayOfWeek object for a localized name and for a number 1-7 for Monday-Sunday per the ISO 8601 standard.

int dowNumber = dow.getValue() ; 

4

String output = dow.getDisplayName( TextStyle.FULL , Locale.CANADA_FRENCH ) ;  // Or Locale.US, Locale.ITALY, etc.

jeudi

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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.

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

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

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.

Where to obtain the java.time classes?

• Java SE 8, Java SE 9, and later
  • Built-in.
  • Part of the standard Java API with a bundled implementation.
  • Java 9 adds some minor features and fixes.
• Java SE 6 and Java SE 7
  • Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
• Android
  • Later versions of Android bundle implementations of the java.time classes.
  • For earlier Android, the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). See How to use ThreeTenABP….

The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, and more.