How to determine if a List is sorted in Java?

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Guava provides this functionality through its Comparators class.

boolean sorted = Comparators.isInOrder(list, comparator);

There’s also the Ordering class, though this is mostly obsolete. An Ordering is a Comparator++. In this case, if you have a list of some type that implements Comparable, you could write:

boolean sorted = Ordering.natural().isOrdered(list);

This works for any Iterable, not just List, and you can handle nulls easily by specifying whether they should come before or after any other non-null elements:

Ordering.natural().nullsLast().isOrdered(list);

Also, since you mentioned that you’d like to be able to check for reverse order as well as normal, that would be done as:

Ordering.natural().reverse().isOrdered(list);

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