Re: Hash or Tree
Wojtek wrote:
Thank-you for all for responding
Philipp wrote :
Wojtek wrote:
Also, if you want to optimize further, and you know you have a well
distributed hashCode (which is the case for the String class), you may
copy the code of HashMap and remove the call to the hash(int h)
method which serves only to prevent very bad hashes to alter the
HashMap's performance prohibitively.
If I do not use the call, how could its removal speed thihgs up? I only
fill the HashMap up once, when the app starts. It NEVER gets any more
values put in.
The internal code of HashMap for get(Object key) (which is the method
you call very often) looks like this:
public V get(Object key) {
if (key == null)
return getForNullKey();
int hash = hash(key.hashCode());
for (Entry<K,V> e = table[indexFor(hash, table.length)];
e != null;
e = e.next) {
Object k;
if (e.hash == hash && ((k = e.key) == key || key.equals(k)))
return e.value;
}
return null;
}
Note in particular that the hashcode of the key is hashed once again by
the hash(int) method. If you have a well distributed hashCode, you can
forget about this step and implement a get which uses the hashCode of
the String directly.
I don't know if this will speed things up significantly, although if you
happen to measure it, please post your results.
Phil