Collection — the root of the collection hierarchy. A collection represents a group of objects known as its elements.

Set — a collection that cannot contain duplicate elements (no consept of order).

List — an ordered collection (sometimes called a sequence). Lists can contain duplicate elements.

Queue — a collection used to hold multiple elements prior to processing.Queues typically, but do not necessarily, order elements in a FIFO (first-in, first-out) manner. Among the exceptions are priority queues.

Map — an object that maps keys to values. A Map cannot contain duplicate keys; each key can map to at most one value.

SortedSet — a Set that maintains its elements in ascending order. Sorted sets are used for naturally ordered sets, such as word lists and membership rolls.

SortedMap — a Map that maintains its mappings in ascending key order. Sorted maps are used for naturally ordered collections of key/value pairs, such as dictionaries and telephone directories