Hi,

This depends on the value of the GeneralFormat, FirstDayOfMonthFormat, and FirstDayOfYearFormat properties in the Calendar.MonthSettings.DaySettings object. These properties vary across themes and in Vista they are all set to "d ", which displays only the day number. Set these properties to "EEE, d" to also display the abbreviated day name:

calendar.getMonthSettings().getDaySettings().setGeneralFormat("EEE, d");
calendar.getMonthSettings().getDaySettings().setFirstDayOfMonthFormat("EEE, d");
calendar.getMonthSettings().getDaySettings().setFirstDayOfYearFormat("EEE, d"); 

Let me know if this helps.

Regards,
Meppy