Iteration order of HashSet

Question

If every object added to a java.util.HashSet implements Object.equals() and Object.hashCode() in a deterministic fashion, is the iteration order over the HashSet guaranteed

Answer 1

Such assumption cannot be made. The javadoc says that:

This class implements the Set interface, backed by a hash table (actually a HashMap instance). It makes no guarantees as to the iteration order of the set; in particular, it does not guarantee that the order will remain constant over time.

The closest you can get is to use a LinkedHashSet, which maintains the insertion order.