Am 04.03.2010 19:33, schrieb Marek Kozieł:
Hello,
I would suggest:
public int hashCode() {
int h = hash;
if (h == 0) {
h = 0;
char[] val = value;
for (int i = offset, limit = count + i; i != limit; )
h = 31 * h + val[i++];
if (h == 0)
h++;
hash = h;
}
return h;
}
Intersting alternative, but I'm afraid, this is against the spec.
Shifting all 0's to 1 would break String's hash definition: h = 31 * h
+ val[i++].
But personally I would consider:
1. make hash long
2. change method of it's generation to ensure that:
-- in most cases String.concat(...) would be able to determine new
hash from substring hashes so it would be available to set it in
constructor always (with little effort it's possible now).
-- would contains flag (bit) that would tell us if hash is bijection
public boolean equals(Object anObject) {
if (this == anObject) {
return true;
}
if (anObject instanceof String) {
String anotherString = (String)anObject;
if (hash!=anotherString.hash) return false;
only valid if (hash != 0 && anotherString.hash != 0)
if (hash&isHashBijection!=0) return true;
Which integer value should isHashBijection have ?
int n = count;
if (n == anotherString.count) {
char v1[] = value;
char v2[] = anotherString.value;
int i = offset;
int j = anotherString.offset;
while (n-- != 0) {
if (v1[i++] != v2[j++])
return false;
}
return true;
}
}
return false;
}
As you know this would require a lot of work and probably it's not
worth it's effect.
Notice one more thing if we would be able to knew if String is in
intern version, equal could look like:
public boolean equals(Object anObject) {
if (this == anObject) {
return true;
}
if (anObject instanceof String) {
String anotherString = (String)anObject;
if (isIntern()&& anotherString.isIntern()) return false;// we
checked it at first line already
int n = count;
if (n == anotherString.count) {
char v1[] = value;
char v2[] = anotherString.value;
int i = offset;
int j = anotherString.offset;
while (n-- != 0) {
if (v1[i++] != v2[j++])
return false;
}
return true;
}
}
return false;
}
Interned strings have their hashes already computed to organize them in
internal hash map. Unfortunately those hashes are not back-propagated to
the Java object, so equals() can't benefit from them for now.
-Ulf
