Why is the Java date API (java.util.Date, .Calendar) such a mess? -


as people painfully aware of now, java api handling calendar dates (specifically classes java.util.date , java.util.calendar) terrible mess.

off top of head:

  • date mutable
  • date represents timestamp, not date
  • no easy way convert between date components (day, month, year...) , date
  • calendar clunky use, , tries combine different calendar systems 1 class

this post sums quite well, , jsr-310 expains these problems.

now question is:

how did these classes make java sdk? of these problems seem obvious (especially date being mutable) , should have been easy avoid. how did happen? time pressure? or problems obvious in retrospect only?

i realize not strictly programming question, i'd find interesting understand how api design go wrong. after all, mistakes learning opportunity (and i'm curious).

someone put better ever it:

  • class date represents specific instant in time, millisecond precision. design of class bad joke - sobering example of how programmers screw up. of methods in date deprecated, replaced methods in classes below.

  • class calendar abstract class converting between date object , set of integer fields such year, month, day, , hour.

  • class gregoriancalendar subclass of calendar in jdk. date-to-fields conversions calendar system in common use. sun licensed overengineered junk taligent - sobering example of how average programmers screw up.

from java programmers faq, version 07.x.1998, peter van der linden - part removed later versions though.

as mutability, lot of jdk classes suffer (point, rectangle, dimension, ...). misdirected optimizations, i've heard say.

the idea want able reuse objects (o.getposition().x += 5) rather creating copies (o.setposition(o.getposition().add(5, 0))) have immutables. may have been idea vms, while it's isn't modern vms.


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