Off Topic: Hidden Features of Java

Question

Happy Friday everyone,
I stumbled upon this conversation on Stack Overflow last night about "hidden" features of Java. Although I knew about most of them (mostly learned from reading posts here in the past few months), thinking about less-often used features of the language is a fun refresher (at least for me).
Can anybody think of any more "hidden" features of Java? Or just something interesting that not many people are familiar with?
Here's the link: [http://stackoverflow.com/questions/15496/hidden-features-of-java|http://stackoverflow.com/questions/15496/hidden-features-of-java]
Edit- To make things a bit more interesting, I'll throw some Dukes at people who show me interesting things.
Edited by: kevinaworkman on Nov 13, 2009 7:56 AM

Answer 1

dcminter wrote:
Here's one I banged my shins on the other day. Comparator may change Set semantics:It's always bothered me that TreeSet relies on Comparator to define equality.
Note that the ordering maintained by a set (whether or not an explicit comparator is provided) must be consistent with equals if it is to correctly implement the Set interface. It bugs me because it's not an explicit requirement of Comparable or Comparable. Therefore, if I did:
set.add("Hello");
System.out.println(set.contains("World"));I would expect false to be printed (in other words, like HashSet, I would expect it to do a final equals() to make sure). But it's not.
However, in your example, it's easy to see why TreeSet could not possibly allow that. If you added 2 Objects that were comparatively equal, it would be impossible to traverse the tree to find anything.