Re: Hash or Tree
Wojtek wrote:
It is being used to hold key/language pairs for making the appliction
internationalization (I18N) aware. So EVERY page hit uses the HashMap
mutilple times:
title
msg to the user about what the page is about
prompt -- help
prompt -- help
propmt -- help
button, button, button
GMT date link to top of page
lcl date copyright
So this small page has 15 language elements, so 15 calls to the HashMap.
The HasMap is the single most used part of the entire app.
I create the menu on app startup and cache it for each language as that
would add 70 or so language elements if it was not cached.
So yes, I have spent a little time trying to make it faster.
But is it actually a bottleneck? I wrote the small program below which
creates a map with 5000 entries, which it then iterates over, and adding
the string lengths (to make sure not too much is optimized away by
hotspot). I start one thread per cpy, and on my Core 2 Quad 2.4 GHz I
get about 40 million lookups (including the &, the sum and length()) per
core.
<sscce>
import java.util.HashMap;
import java.util.Map;
public class HashMapSpeed implements Runnable {
private static final int RUNS = 50;
private static final int LOOPS = 10000000;
private Map<String,String> map;
private String[] keys;
public static void main(String...arg) {
HashMapSpeed hms = new HashMapSpeed();
for (int i = 0; i < Runtime.getRuntime().availableProcessors();
i ++) {
new Thread(hms).start();
}
}
public void run() {
for(int i = 0; i < RUNS; i ++) {
long start = System.nanoTime();
int sum = doIt(LOOPS);
long delta = System.nanoTime() - start;
System.err.format("Loops/s %.0f dummy %s%n", LOOPS *
1000000000d / delta, sum);
}
}
public HashMapSpeed() {
keys = new String[5000];
map = new HashMap<String,String>();
for (int i = 0; i < keys.length; i ++) {
keys[i] = "key-"+i;
map.put(keys[i], "Some fairly Long String " + i);
}
}
public int doIt(int times) {
int sum = 0;
for (int i = 0; i < times; i++) {
sum += map.get(keys[i % 0xfff]).length();
}
return sum;
}
}
</sscce>
--
Roger Lindsj?