The Set interface exactly fits into collections interfaces hierarchy and thereby it is a part of collections framework. The very very important characteristic of Set is it does not allow duplicate elements. It allows null elements. But it permits only one null element as set does not allow duplicates. The Set interfaces comes with two important subclasses – HashSet and TreeSet. HashSet constructors are overloaded that can take different capacities and load factors. TreeSet object cannot be created as tree is balanced always.
Following is the interface signature
The Set interface does not add any new methods but overridden many methods of Collection interface with its own functionality.