1 Collections Collections A Collection allows a group of objects to be treated as a single unit.
Collections define a set of core interfaces.
These are - Collection Set List SortedSet Map SortedMap Collections also provide implementation for these interfaces. The Object hierarchy of Core Interfaces defined in Collections is given below. The Collection interface is the root of Collection hierarchy, and is used for common functionality across all collections. There is no direct implementation of Collection interface. The Set interface is used to represent a group of unique elements.