How can i generate a long hash of a String?

Question

I have a java applciation in which I want to generate long ids for strings (in order to store those strings in neo4j). In order to avoid data duplication, I would like to generate an id for each string stored in a long integer, which should be unique for each string. How can I do that ?

Answer 1

long has 64 bits. A String of length 9 has 72 bits. from pigeon hole principle - you cannot get a unique hashing for 9 chars long strings to a long.

If you still want a long hash: You can just take two standard [different!] hash functions for String->int, hash1() and hash2() and calculate: hash(s) = 2^32* hash1(s) + hash2(s)