Calendar c = Calendar.getInstance();
c.set(Calendar.MONTH, month); // 0-based
c.set(Calendar.YEAR, year);

Calendar cal = Calendar.getInstance();
cal.set(Calendar.YEAR, year);
cal.set(Calendar.MONTH, month);

Calendar calendar = Calendar.getInstance();
calendar.set(Calendar.MONTH, Calendar.MAY); // note this is a 0-11 value for jan-dec
calendar.set(Calendar.DATE, 20); // pick the 20th day...or whatever from input

YearMonth ym = YearMonth.of( 2017 , Month.MARCH );

LocalDate firstOfMonth = ym.atDay( 1 );
LocalDate endOfMonth = ym.atEndOfMonth();

List<LocalDate> dates = new ArrayList<>( 31 );
LocalDate localDate = ym.atDay( 1 );
while ( YearMonth.from( localDate ).equals( ym ) {
    dates.add( localDate );
    // Set up the next loop.
    localDate = localDate.plusDays( 1 );
}