The java.util.Set interface and related implementations dont
support duplicate elements.

in java .util package there is one interface (set interface)
that interface does not allows the duplicate values.that 
interface implementations class are 
hashset,treeset....these classes don't allow the duplicate 
values.

java.util.Set Packages, there is no dulicate elements.Bcoz 
these interfaces doesn't allows the dulicate values or 
elements. For example. HashMap, HashSet, TreeSet and so on.

Which one will not allow duplicates, is it HashMap or 
HashTable? Please explain the corect answer with an 
example. Thanks in advance

HashSet

set wont allow duplicate element all the classes implementin
set interface wont allow for eg HashSet TreeSet
Hash map will allow for two different key u can have same value

the set inteface does'nt allow duplicate 
elements.therefore,the add() method return false if an 
attempt is made to add duplicate elements to a set.

hashset,treeset....these classes don't allow the duplicate 
values.