vm optimizations

From: Murat Tasan (tasan_at_eecs.cwru.edu)
Date: 10/30/03 

Date: Wed, 29 Oct 2003 22:46:04 -0500

i asked something about java optimization before, but i gave a very poor
example... leading to not much help... so here is a better situation.

i have a Map, and i'm constantly picking entries from random from this
map.

in one method, i only use the map.
in another method, i use an array of keys from the map, stored seperately.

method a (only the map):

Map myMap = //initialize map
Object randObj;
// begin loop
randObj = myMap.keySet().toArray()[(int)Math.floor(Math.random() *
myMap.size())];

so, as you can see, in method a i constantly re-acquire the array of
keys... but reduce the clutter.

method b:

Map myMap = //initialize map
Object[] keyArray = myMap.keySet().toArray();
// begin loop
randObj = myMap.get(keyArray[(int)Math.floor(Math.random() *
keyArray.length)]);

the only change then is one single array that has a name.

what i'm wondering is:

does the compiler or runtime environment do any optimizations such that
method a is the same (or better maybe) than method b?

while i know the call stack will be one shorter in method b, i'm really
curious about whether or not method a constantly allocates and frees up
memory for the array.

does anyone know where i can find out about these sorts of issues, or can
anyone clear this example out for me?

thanks much,

murat 

-- 
Murat Tasan
mxt6@po.cwru.edu
tasan@eecs.cwru.edu
murat.tasan@cwru.edu
http://genomics.cwru.edu

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