Re: string case clauses
On 9/14/2011 12:13 PM, Roedy Green wrote:
On Sun, 11 Sep 2011 20:05:20 -0700, Peter Duniho
<NpOeStPeAdM@NnOwSlPiAnMk.com> wrote, quoted or indirectly quoted
someone who said :
Huh? How so? It's actually basically the same algorithm a full-on hash
table would use. Specifically: hash value gets you to a very small
subset of the possible values (very often just one, as long as the hash
code algorithm is good), then linear search on collisions.
Before case strings, there were two JVM instructions for implementing
an int switch, tableswitch and lookupswitch. The efficient tableswitch
is a jump table used when the switch values are reasonably dense e.g.
numbered 0..N. The less efficient lookupswitch is a binary search or
linear search used when the switch values all over the map.
I understood the way string case labels worked posted earlier was to
use the hashCode as the switch variable, which would necessitate the
use of the inefficient lookupswitch plus a little kludge to deal with
hashCode collisions.
Why do you assume it would be inefficient? If the number of cases is
small, a linear search may well be faster than a HashMap lookup. If the
number of cases is large, wouldn't it use a binary search?
However, I don't like switch statements with a lot of cases anyway,
because of unreadability and maintenance issues.
Patricia