Deadly trap all Java programmers should know: URL.equals() and
URL.hashCode() resolve the hostname in the URL, then compare equality
by IP address. Which means 1) these methods are way too slow and 2)
virtual hosts break them – every RSS feed URL on blogspot.com (for
example) compares equal.
(This post was originally found at http://log.ometer.com/2006-08.html#12)