Java equivalent of Python 'in' - for set membership test?

You can't do it with a straight array, but you can with a Set<T> by calling .contains. If you feel like you will be doing a lot of isItemInSet calls, consider using Sets instead of arrays -- you will be much happier.

For example, using a HashSet<T> makes isItemInSet an O(1) operation (on average). Set insertion and deletion are also similarly fast. Indeed, a HashSet<T> in Java is essentially the same as a Python set() (similar underlying concept and performance characteristics) -- you will see a big improvement in speed with many calls to query, insert or delete on the set.