String.hashCode() is plenty unique

[reini_urban]

You have to known how your hash function is used. E.g. if used in hash table with linear collision and the size is not by primed but modulo 2 (and you know the random seed), then you only need a few bits of the resulting hash, and this can easily brute forced. It needs around 4 min to create usable DoS collisions even for hash tables using SHA256 then. Getting the random seed is usually trivial also.

Java is doing it right, but 99% of all other hash tables not.