shinnlok/liferay-portal — comment on commit b5b7865c23331983d32e8fa045443e76bccdd17f
File:  line 0
By shinnlok:

This is assuming that day, month or year can be individually inputted.

ie:
Day: 5
Month: August
Year: Null
->
Day: 5 + delta
Month: August + delta
Year: Default + delta

Changing the day could affect month or year, changing month could only affect year, and changing the year doesn't affect anything else. This also does not account for leap years, months with different # of days.. etc.