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No of Days in month

Posted on 2000-05-11
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Last Modified: 2010-04-01
I wanna know if there is any methods in API which can give the No of days in a given month of the year.
I know writing the code is easier,but just curious.
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Question by:nellore
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Jim Cakalic earned 50 total points
ID: 2802498
Try using the Calendar class. The easiest demonstration is number of days for the current month:

Calendar cal = Calendar.getInstance();
cal.setTime(new Date());
int days = cal.getActualMaximum(Calendar.DAY_OF_MONTH);

You can do the same for any arbitrary date by initializing the Calendar object with a specific date before asking for the maximum:

// set to 1-feb-2000 (month is 0-based)
cal.setTime(2000, 1, 1);

Since Calendar knows leap years, asking for maximum DAY_OF_MONTH will return 29 as 2000 is a leap year.

Best regards,
Jim Cakalic

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by:nellore
ID: 2802515
Thanks for the answer.

Actually
cal.setTime(2000, 1, 0)
is returning the Date set to the last day of Jan(not 0-based).


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Expert Comment

by:sloJava
ID: 2802517
There is not explicit method in the API for doing this.
I came across this clever nugget some where...

int days = 32 - new Date(year, month, 32).getDate();
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Expert Comment

by:maheshsivakumar
ID: 2803880
Yeah the best method should be what jim has stated.
 It gives the maximum no of days of any month if the Calendar object is initialized correctly.
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Expert Comment

by:Jim Cakalic
ID: 2804366
By using set(2000, 1, 0) you have initialized Calendar to the 0th day of month 1 -- the 0th day of February. There is no 0th day of February (or any month) so Calendar normalizes the value on your behalf and ends up with the 31st of January. This is the lenient mode of Calendar. However, do not be misled. Calendar definitely treats months as 0-based, everything else is 1-based. If you have programmed in C/C++, you may recognize this as behavior similar to that surrounding interpretation of struct tm. I never understood why a 0-based month is necessary but I have come to accept it. One way to verify this is to look at the values of the month constants in Calendar (JANUARY, FEBRUARY, ...). If you don't have the code, you can simply print the values:

    system.out.println("Jan = " + Calendar.JANUARY);
    System.out.println("Dec = " + Calendar.DECEMBER);

This fragment of code will print:

    Jan = 0
    Dec = 11

You can disable the ability to initalize Calendar with "invalid" dates by changing the lenient mode. The following bit of code will result in an InvalidArgumentException.

    Calendar cal = Calendar.getInstance();
    cal.setLenient(false);
    cal.set(2000, 1, 0);

Best regards,
Jim Cakalic
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