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Added javadoc to explain the quandry in how to count month/day differences 

git-svn-id: https://svn.apache.org/repos/asf/jakarta/commons/proper/lang/trunk@483891 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Henri Yandell 2006-12-08 09:05:52 +00:00
parent 1554d439a5
commit ee4ad2727f
1 changed files with 16 additions and 6 deletions
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22
src/java/org/apache/commons/lang/time/DurationFormatUtils.java
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@ -249,7 +249,18 @@ public class DurationFormatUtils {
/**
* <p>Formats the time gap as a string, using the specified format.
* Padding the left hand side of numbers with zeroes is optional and
* the timezone may be specified.
* the timezone may be specified. </p>
*
* <p>When calculating the difference between months/days, it chooses to
* calculate months first. So when working out the number of months and
* days between January 15th and March 10th, it choose 1 month and
* 23 days gained by choosing January->February = 1 month and then
* calculating days forwards, and not the 1 month and 26 days gained by
* choosing March -> February = 1 month and then calculating days
* backwards. </p>
*
* <p>For more control, the Joda Time library is recommended
* (<a href="http://joda-time.sf.net/"). </p>
*
* @param startMillis the start of the duration
* @param endMillis the end of the duration
@ -304,11 +315,10 @@ public class DurationFormatUtils {
while (days < 0) {
end.add(Calendar.MONTH, -1);
days += end.getActualMaximum(Calendar.DAY_OF_MONTH);
//days += 31; // TODO: Need tests to show this is bad and the new code is good.
// HEN: It's a tricky subject. Jan 15th to March 10th. If I count days-first it is
// 1 month and 26 days, but if I count month-first then it is 1 month and 23 days.
// Also it's contextual - if asked for no M in the format then I should probably
// be doing no calculating here.
// HEN: It's a tricky subject. Jan 15th to March 10th. If I count days-first it is
// 1 month and 26 days, but if I count month-first then it is 1 month and 23 days.
// Also it's contextual - if asked for no M in the format then I should probably
// be doing no calculating here.
months -= 1;
end.add(Calendar.MONTH, 1);
}