How to get the first day of the current week and month?

Question

I have the date of several events expressed in milliseconds[1], and I want to know which events are inside the current week and the current month, but I can't figure out how to obtain the first day (day/month/year) of the running week and convert it to milliseconds, the same for the first day of the month.

[1]Since January 1, 1970, 00:00:00 GMT 

Answer 1

This week in milliseconds:

// get today and clear time of day Calendar cal = Calendar.getInstance(); cal.set(Calendar.HOUR_OF_DAY, 0); // ! clear would not reset the hour of day ! cal.clear(Calendar.MINUTE); cal.clear(Calendar.SECOND); cal.clear(Calendar.MILLISECOND);  // get start of this week in milliseconds cal.set(Calendar.DAY_OF_WEEK, cal.getFirstDayOfWeek()); System.out.println("Start of this week:       " + cal.getTime()); System.out.println("... in milliseconds:      " + cal.getTimeInMillis());  // start of the next week cal.add(Calendar.WEEK_OF_YEAR, 1); System.out.println("Start of the next week:   " + cal.getTime()); System.out.println("... in milliseconds:      " + cal.getTimeInMillis()); 

This month in milliseconds:

// get today and clear time of day Calendar cal = Calendar.getInstance(); cal.set(Calendar.HOUR_OF_DAY, 0); // ! clear would not reset the hour of day ! cal.clear(Calendar.MINUTE); cal.clear(Calendar.SECOND); cal.clear(Calendar.MILLISECOND);  // get start of the month cal.set(Calendar.DAY_OF_MONTH, 1); System.out.println("Start of the month:       " + cal.getTime()); System.out.println("... in milliseconds:      " + cal.getTimeInMillis());  // get start of the next month cal.add(Calendar.MONTH, 1); System.out.println("Start of the next month:  " + cal.getTime()); System.out.println("... in milliseconds:      " + cal.getTimeInMillis());