Is there any method in Java Date-Time API to get collection of all days in a week?

Question

I want names of all days in a week, but i have to create Enum(can be achieved by other ways too).

Another way is to get the constant from calendar class and store them manually in Collection.

But, Is there any method in Java Date-Time API to get Collection of all Days name in a week or Collection of all months name in year.

Answer 1

Yes you can using DateFormatSymbols :

DateFormatSymbols symbols = new DateFormatSymbols(new Locale("en"));
String[] days = symbols.getWeekdays();
String[] months = symbols.getMonths();

There are also methods for short names (for en it would be Sat etc.) and of course you can choose your locale. Works with Java 1.6+.

@Edit: as to why this returns 8 values for days, if you check the Calendar class they start counting days from 1 to 7 so I guess DateFormatSymbols doesn't want to fool around with subtracting one and they just went with an array of size 8.

@Edit2: in the source code you can see:

 * Weekday strings. For example: "Sunday", "Monday", etc.  An array
 * of 8 strings, indexed by <code>Calendar.SUNDAY</code>,
 * <code>Calendar.MONDAY</code>, etc.
 * The element <code>weekdays[0]</code> is ignored.

So as I said they are simply using Calendar values as indices, that's all.

Answer 2

Java SE 8及更高版本提供了枚举：

• DayOfWeek
• Month

Answer 3

Using java.time

The Answer by Puce is correct, but brief. I'll add more detail.

DayOfWeek & Month enums

The java.time classes include DayOfWeek and Month enum classes. An enum means they pre-define several objects. In this case we already have seven objects in DayOfWeek , one for each day of the week. And we have a dozen Month objects already defined for January-December.

EnumSet

Java also provides a highly optimized implementation of Set for collecting enum objects, EnumSet , to use very little memory while executing extremely fast.

If you want just the weekend, you can define a pair of days in a set.

Set<DayOfWeek> weekend = EnumSet.of( DayOfWeek.SATURDAY , DayOfWeek.SUNDAY ) ;

In your case we want all seven days.

Set<DayOfWeek> days = EnumSet.allOf( DayOfWeek.class );

Localize

When you want to see strings for the names of the day, ask. Automatically localize by calling getDisplayName . Specify how long or abbreviated you want the name. Pass a Locale to determine the human language to use in translating the name of the day.

for( DayOfWeek dow : days ) {
    String output = dow.getDisplayName( 
                        TextStyle.FULL , 
                        Locale.CANADA_FRENCH 
                    ) ;
}

You can do all the same stuff for Month .

Set<Month> months = EnumSet.allOf( Month.class );
for( Month month : months ) {
    String output = month.getDisplayName( 
                        TextStyle.FULL , 
                        Locale.CANADA_FRENCH 
                    ) ;
}

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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 .

Where to obtain the java.time classes?

• Java SE 8 and 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 SE 7
  • Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport .
• Android
  • The ThreeTenABP project adapts ThreeTen-Backport (mentioned above) for Android specifically.
  • 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 .