Using hashcode for a unique ID

Question

I am working in a java-based system where I need to set an id for certain elements in the visual display. One category of elements is Strings, so I decided to use the String

Answer 1

Hashes are not unique, hence they are not apropriate for uniqueId.

As to probability of hash collision, you could read about birthday paradox. Actually (from what I recall) when drawing from an uniform distribution of N values, you should expect collision after drawing $\sqrt(N)$ (you could get collision much earlier). The problem is that Java's implementation of hashCode (and especially when hashing short strings) doesnt provide uniform distribution, so you'll get collision much earlier.