Why doesn't String's hashCode() cache 0?
- by polygenelubricants
I noticed in the Java 6 source code for String that hashCode only caches values other than 0. The difference in performance is exhibited by the following snippet:
public class Main{
static void test(String s) {
long start = System.currentTimeMillis();
for (int i = 0; i < 10000000; i++) {
s.hashCode();
}
System.out.format("Took %d ms.%n", System.currentTimeMillis() - start);
}
public static void main(String[] args) {
String z = "Allocator redistricts; strict allocator redistricts strictly.";
test(z);
test(z.toUpperCase());
}
}
Running this in ideone.com gives the following output:
Took 1470 ms.
Took 58 ms.
So my questions are:
Why doesn't String's hashCode() cache 0?
What is the probability that a Java string hashes to 0?
What's the best way to avoid the performance penalty of recomputing the hash value every time for strings that hash to 0?
Is this the best-practice way of caching values? (i.e. cache all except one?)
For your amusement, each line here is a string that hash to 0:
pollinating sandboxes
amusement & hemophilias
schoolworks = perversive
electrolysissweeteners.net
constitutionalunstableness.net
grinnerslaphappier.org
BLEACHINGFEMININELY.NET
WWW.BUMRACEGOERS.ORG
WWW.RACCOONPRUDENTIALS.NET
Microcomputers: the unredeemed lollipop...
Incentively, my dear, I don't tessellate a derangement.
A person who never yodelled an apology, never preened vocalizing transsexuals.
