Tough Calendar class questions

[Peter Wipperfurth]

Hello,

I have two really tough Calendar class questions that
resemble word problems (two variables known, third unknown).

first
You have month and year (integer format).
How many days were in that month?
Example: 10/2005,4/2004,6/2006

second
You have week and year (integer format)
What month does it refer to?
Example: week5,week10,week32,week40 and 2006,2005,2002

I'm not familiar with Calendar classes but it seems you would create a calendar object, set the month and year, generate milliseconds...then I'm stuck.

Any ideas?

[Keith Lynn]

Peter, I would recommend looking at the API docs for the Calendar class.

[Peter Wipperfurth]

Originally posted by Keith Lynn:
I would recommend looking at the API docs for the Calendar class.

Thanks Keith, found a solution on the web for the second problem:

import java.util.Calendar;

class weektst
{
public static Calendar c=Calendar.getInstance();

public static Calendar setwk(Calendar c,int woy,int year)
{
System.out.println("for week: " + woy + " and year:" + year);
c.set(Calendar.YEAR,year);
c.set(Calendar.WEEK_OF_YEAR,woy);
System.out.println("date: " + c.getTime());
System.out.println("week: " + c.get(Calendar.WEEK_OF_YEAR));
System.out.println();
return c;
}

public static void main(String[] args)
{
c=setwk(c,5,2004);
c=setwk(c,10,2004);
c=setwk(c,32,2005);
c=setwk(c,40,2006);
}
}

From there you simply parse out the month...

Peter
[ July 05, 2006: Message edited by: Peter Wipperfurth ]

[Peter Wipperfurth]

Originally posted by Peter W.:
You have month and year (integer format).
How many days were in that month?
Example: 10/2005,4/2004,6/2006

There are apparently nuances to using the Calendar class with exact precision. Following is a solution that is approximate:

import java.util.Calendar;
import java.util.GregorianCalendar;

class daysin_month
{
public static Calendar c;
public static Calendar setmy(int m,int y)
{
Calendar tmpc=new GregorianCalendar(y,m,1);

System.out.println("max days in month: " + m + " in year: " + y);
System.out.println("month: " + m);
System.out.println("year: " + y);
System.out.println("max days: " + tmpc.getActualMaximum(Calendar.DAY_OF_MONTH));
return tmpc;
}

public static void main(String[] args)
{
c=setmy(10,2005);
c=setmy(4,2004);
c=setmy(6,2006);
}
}

However, the third result (June 2006) has too many days:

max days in month: 6 in year: 2006
month: 6
year: 2006
max days: 31

What modifications are needed to return correctly?

Peter
[ July 05, 2006: Message edited by: Peter Wipperfurth ]

[Andy T�pfer-Hinz]

I think this is correct as the months are counted from 0 to 11,
so month 6 is july which has 31 days !

[Peter Wipperfurth]

so month 6 is july which has 31 days !

Thanks!

[Wu Kong]

For Gregorian calendar,
1) Find the max. # of days for a particular month - solution is avaliable

Calendar cal = new GregorianCalendar(2006, 7-1, 1);
System.out.println(cal.getActualMaximum(Calendar.DAY_OF_MONTH));

2)
Find the month, given the week # in a year - not easy. A week may span two months. However, it is possible to find out the 1st day of Week #xx is in which month, for a particular calendar year.

int WEEK_NO = 10; int YEAR=2005;
Calendar cal = new GregorianCalendar(YEAR, 1 - 1, 1);
cal.setLenient(true);
for (int i = 0; i < 53; i++) {
  int weekNo = cal.get(Calendar.WEEK_OF_YEAR);
  if(weekNo == WEEK_NO) {
    System.out.println("Month=" + (cal.get(Calendar.MONTH)+1) + " -" + cal.getTime());
    // got it. returns.
  }
  cal.add(Calendar.DATE, 7);
}

NB: Please check getFirstDayOfWeek() and getMinimalDaysInFirstWeek().
[ July 06, 2006: Message edited by: Wu Kong ]