Generate a random and reproducable hashcode for a string comparable to ora_hash

I have the requirement to generate random but reproducible numbers for arbitrary strings in Java. For the same requirement in SQL I have used the function ORA_HASH provided by Oracle:

ORA_HASH generates hash values for an expression. You can use it to randomly assign a set of values into several buckets for analysis, or to generate a set of random numbers.

The function has three parameters: the expression to hash, the maximum bucket number, and a seed. For my purposes in SQL the maximum bucket number has been set to the maximum allowed value.

My idea is to implement ORA_HASH in Java (with maximum bucket number). For that purpose I want to combine String.hashCode() with a random seed.

However, I have no idea how to combine the hashcode and the seed such that

1. no additional hash collision emerges (xor probably don't satisfy this requirement)
2. neither the seed nor the original expressions are (easily) reproducible from the result (a simple + don't satisfy this requirement)

Any idea for a better solution?