For the hashCode of an int the most natural choice is to use the int itself. A better question is what to use for the hashCode of a long since it doesn’t fit into the int-sized hashcode. Generally, your best source for that—and all hashCode-related questions—would be Effective Java.
Here’s what Effective Java recommends (and the JDK uses) for the long type:
(int) (value ^ (value >>> 32))