I need to get a list of days each month in the JODA library. how can I do that?

tl;dr

Using java.time, the successor to Joda-Time.

yearMonth               // An instance of `java.time.YearMonth`.
.atDay( 1 )             // Returns a `LocalDate` object for the first of the month.
.datesUntil(            // Get a range of dates.
    yearMonth
    .plusMonths( 1 )    // Move to the following month.
    .atDay( 1 )         // Get the first day of that following month, a `LocalDate` object.
)                       // Returns a stream of `LocalDate` objects.
.toList()               // Collects the streamed objects into a list. 

For older versions of Java without a Stream#toList method, use collect( Collectors.toList() ).

java.time

The Joda-Time project is now in maintenance mode. The project recommends moving to its successor, the java.time classes defined in JSR 310 and built into Java 8 and later. Android 26+ has an implementation. For earlier Android, the latest Gradle tooling makes most of the java.time functionality available via « API desugaring ».

YearMonth

Specify a month.

YearMonth ym = YearMonth.now() ;

Interrogate for its length.

int lengthOfMonth = ym.lengthOfMonth() ;

LocalDate

To get a list of dates, get the first date of the month.

LocalDate start = ym.atDay( 1 ) ;

And the first day of the next month.

LocalDate end = ym.plusMonths( 1 ).atDay( 1 ) ;

Get a stream of dates in between. Collect into a list.

List< LocalDate > dates = start.datesUntil( end ).toList() ;