Calendar Problem

[kvass]

Hey guys I'm working on a program that asks the user to enter a month and year and then prints that month's calendar page on the screen. However, to do this I created a daysBetween() method that accepts 2 dates and finds the number of days between them. So basically I need some advice for subtracting 2 dates and finding the days between them... I don't want code but just general ideas for algorithms or approaches I could use. Because it's proving to be much more difficult to implement than I previously thought.

Thanks so much!
~Kvass

[NormR1]

Create Calendar objects, get the epoch times for each, subtract and divide.

[kvass]

epoch times?

Please be more specific. I don't need code, but I need more thorough explanation.

[NormR1]

epoch times

Ask Google or read the API doc for Date or Calendar.

Which part don't you understand?
Use SimpleDateFormat to get a Date object for the two dates.
Get the epoch times for each date.
Subtract the times
Convert the time difference to days.

[kvass]

Ok -- but I was kind of hoping to solve this problem on my own without the assistance of other objects (aside from Scanner for user input). Because I would rather understand the mathematical or algorithmic approach to this problem rather than just use an object that someone else made for me.

[NormR1]

Go ahead and write as much code as you want.
I've reinvented a few wheels in my time. You learn sometimes. Other times, you just waste time.

[kvass]

Ok -- so can some1 help give me a pointer on reinventing this wheel?

I need some advice for subtracting 2 dates and finding the days between them... I don't want code but just general ideas for an algorithm I could use. Because it's proving to be much more difficult to implement than I previously thought. And I don't want to use the Calendar and Date classes predefined in the Java API.

[NormR1]

Starting at older date, add one day to it and see if it is the end date.
Define a class that defines a date as day, month, year.
Add methods to it:
to add a day and
to compare against another date

[JamesCherrill]

Or:
Write a method to convert a date (int yyyy, int mm, int dd) to the number of days after Jan 1st 1900 (or some other convenient earliest date) - something along the lines of

int daysAfterJan1st1900(int yyyy, int mm, int dd) {
  return (yyyy - 1900)*365 + (something for leap years) + (number of days in each month up to mm) + dd;
}

Once you have written this, then you can trivially convert both your dates to days after 1/1/1900 and subtract them. You can also get day of the week by just calculating %7 on that.
(This is how date libraries usually work.)

[uday_123]

Is there any problem for 1900 in java calender.
I am trying to add 1900 but it gives error

[JamesCherrill]

No problem (except that it's not a leap year, even tho it's divisible by 4).