The collection libraries have a uniform approach to equality and hashing. The idea is, first, to divide collections into sets, maps, and sequences. Collections in different categories are always unequal. For instance, Set(1, 2, 3) is unequal to List(1, 2, 3) even though they contain the same elements. On the other hand, within the same category, collections are equal if and only if they have the same elements (for sequences: the same elements in the same order). For example, List(1, 2, 3) == Vector(1, 2, 3), and HashSet(1, 2) == TreeSet(2, 1).
This is a companion discussion topic for the original entry at http://docs.scala-lang.org//overviews/collections/equality