Question

Is it possible to subtract time from a calendar?

e.g.

.....
Calendar DueTime      = Calendar.getInstance();
Calendar ReminderTime = Calendar.getInstance();

int ReminderMinute = 5;

DueTime.set(DueYear, DueMonth, DueDay, DueHour, DueMinute);

    Day   = Day   - reminderDays   ;
    Day   = Day   - (Week*7)       ;
    Month = Month - reminderMonths ;
    Year  = Year  - reminderYears  ;
    Hour  = Hour  - reminderHours  ;
    Minute= Minute- reminderMinutes;

    ReminderTime.set(Year, Month, Day, Hour, Minute  );
    ReminderTime.add(Calendar.DAY_OF_MONTH , - Day   );
    ReminderTime.add(Calendar.MONTH        , - Month );
    ReminderTime.add(Calendar.YEAR         , - Year  );
    ReminderTime.add(Calendar.HOUR         , - Hour  );
    ReminderTime.add(Calendar.MINUTE       , - Minute);

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If the above is possible another question I would like to know is if…

reminderDays = 60;

Then would that go into the month before it as well?

Say its the 31st of the month that the due date is and the month before it has 30 days would the reminder day be the 1st of that month?

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On another note that’s related:

I’m not sure if I am right or not but does a calendar instance store time in milliseconds?

e.g. 1 minute would be 600 milliseconds and an hour would be 36000 milliseconds

So if I did:

ReminderTime.add(Calendar.HOUR         , - 1  );

all it would be doing is adding -36000 to the total time stored in that calendar object

so if that’s true would doing:

ReminderTime.add(Calendar.DAY_OF_MONTH , - 60   );

result in it subtracting 51840000 milliseconds? Or would I need to change

ReminderTime.add(Calendar.DAY_OF_MONTH , - 60   );

to

ReminderTime.add(Calendar.DAY_OF_YEAR  , - 60   ); 

This would be after I call:

ReminderTime.set(Year, Month, Day, Hour, Minute  );

What I expect from this above is that my activity will calculate which day of the year that calendar object is and remove 51840000 milliseconds from it.

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Can anyone help?

Three different questions here, separated by lines

Answer 1

Three questions, two statements which should enable you to answer them yourself.

1) Yes you can subtract by adding a negative number as you have written.

2) The fields carry, just like units,tens,hundreds do. So taking 60 off the DAY_OF_MONTH will carry into the previous month or months or year if necessary. It will adjust the calendar by 60 days

P.S. 1 minute isn’t 60 milliseconds! It’s 60 x 1000 = 60,000 milliseconds