set stores elements in an unordered way but does not 
contain duplicate elements,where as ist stores elements in 
an ordered way but may contain duplicate elements.

set-->
when uniqueness is required you need to implement set.
e.g.
HashSet(unOrd,unSort) Fast access, assures no duplicates,
provides no ordering.
LinkedHashSet(Ord,unSort)No duplicates; iterates by
insertion order.
TreeSet(ascending,naturalord)No duplicates ; iterates in
sorted order.

list-->
when ordered list is required you need to implement list.
e.g.
ArrayList(Ord,unSort)Fast iteration and fast random access.
Vector(syncronized)
LinkedList()Good for adding elements to the ends, i.e.,
stacks and queues.

set stores elements in an unordered way but does not 
contain duplicate elements,where as it stores elements in 
an ordered way but may contain duplicate elements.