For GregorianCalendar, why isLeapYear(int year)? I think shoud be isLeapYear()!

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www - 15 Jul 2007 20:26 GMT

Hi,

In GregorianCalendar, I don't understand why isLeapYear method needs an
argument. e.g.

Calendar cal = new GregorianCalendar();
cal.set(bla.. bla .. bla); //set time

//check if the time represent by cal is a leap year
if(cal.isLeapYear()) { ... } //oops, wrong, need to be

if(cal.isLeapYear(cal.get(Calendar.YEAR))) { ... } //!!! I don't
understand, why need "cal" twice to check if cal is in a leap year

Thank you for your help.

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Eric Sosman - 15 Jul 2007 21:14 GMT

> Hi,
>
[quoted text clipped - 9 lines]
> if(cal.isLeapYear(cal.get(Calendar.YEAR))) { ... } //!!! I don't
> understand, why need "cal" twice to check if cal is in a leap year

You may be surprised to learn that the code you have
posted won't compile, even when placed in a suitable context
and with its `...' fleshed out. The Calendar class has no
isLeapYear() method at all, so `cal' cannot invoke it.

As for the isLeapYear() method of GregorianCalendar,
sometimes you want to decide whether the calendar's current
year is or isn't a leap year -- that's what you've tried
to show -- but sometimes you want to ask the same question
about some other year. In that case, you get to choose
between

    GregorianCalendar cal = new GregorianCalendar();
    if (cal.isLeapYear(2000)) ... // as things stand

and

    GregorianCalendar cal = new GregorianCalendar();
    cal.set(Calendar.YEAR, 2000);
    if (cal.isLeapYear()) ... // fictional method

or

    GregorianCalendar cal = new GregorianCalendar(
    2000, Calendar.JANUARY, 1);
    if (cal.isLeapYear()) ... // fictional method

Signature

Eric Sosman
esosman@ieee-dot-org.invalid

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Roedy Green - 15 Jul 2007 22:19 GMT

>if(cal.isLeapYear(cal.get(Calendar.YEAR))) { ... } //!!! I don't
>understand, why need "cal" twice to check if cal is in a leap year

You are right. isLeap() should be an instance method and isLeap(
yyyy) should be a static method. This is par for the course. The
folks who did Date and Calendar are not the best programmers.

This is the least of their problems. See
http://mindprod.com/jgloss/date.html
http://mindprod.com/jgloss/calendar.html

Signature

Roedy Green Canadian Mind Products
The Java Glossary
http://mindprod.com

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Stefan Ram - 15 Jul 2007 22:28 GMT

>You are right. isLeap() should be an instance method and isLeap(
>yyyy) should be a static method.

I did it this way in my library:

The instance method:

http://www.purl.org/stefan_ram/html/ram.jar/de/dclj/ram/type/gregorian/Year.html
#isLeapYear()

The static method:

http://www.purl.org/stefan_ram/html/ram.jar/de/dclj/ram/algorithm/gregorian/Year
.html#isLeapYear(int)

The implementation of the instance method is based on the
static method:

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For GregorianCalendar, why isLeapYear(int year)? I think shoud be isLeapYear()!

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