To get a week number of a specific date use the Calendar.Week_of_year. To get the week numbers of a certain month run through each day of the month. You can do something like this, calling the function for a the specific month and year and String in return with the week number for each day.
When using the Calendar class in Android Java the default start of the week is Sunday. To change this use the following function setFirstDayOfWeek Calendar cal; cal.setCalendar(Calendar.getInstance()); cal.setFirstDayOfWeek(Calendar.MONDAY); cal.getInstance() set it to the current date. setFirstDayOfWeek takes an integer. Calendar.MONDAY is just an integer value of 1. Sunday has the value 0, Tuesday = 2, Wednesday