user3673623 :
Looking at Java's String class we can see that hash code is cached after first evaluation.
public int hashCode() {
int h = hash;
if (h == 0 && value.length > 0) {
char val[] = value;
for (int i = 0; i < value.length; i++) {
h = 31 * h + val[i];
}
hash = h;
}
return h;
}
Where hash is an instance variable. I have a question, why do we need that h extra variable?
Andremoniy :
Simply because hash value changes in the loop and your solution without intermediate temporary variable is not thread-safe. Consider that this method is invoked in several threads.
Say thread-1 started hash computation and it is not 0 anymore. Some small moment later thread-2 invokes the same method hashCode() on the same object and sees that hash is not 0, but thread-1 hasn't yet finished its computation. As the result, in the thread-2 wrong hash (not fully computed) value will be used.
Guess you like
Origin http://10.200.1.11:23101/article/api/json?id=442483&siteId=1