This interface represents an unordered Collection of objects that contains no duplicate elements. That is, a Set cannot contain two elements e1 and e2 where e1.equals(e2) , and it can contain at most one null element. The Set interface defines the same methods as its superinterface, Collection . It constrains the add( ) and addAll( ) methods from adding duplicate elements to the Set . In Java 5.0 Set is a generic interface and the type variable E represents the type of the objects in the set. An interface cannot specify constructors, but it is conventional that all implementations of Set provide at least two standard constructors: one that takes no arguments and creates an empty set, and a copy constructor that accepts a Collection object that specifies the initial contents of the new Set . This copy constructor must ensure that duplicate elements are not added to the Set , of course. As with Collection , the Set methods that modify the contents of the set are optional, and implementations that do not support the methods throw java.lang.UnsupportedOperationException . See also Collection , List , Map , SortedSet , HashSet , and TReeSet . Figure 16-54. java.util.Set<E>public interface Set<E> extends Collection<E> { // Public Instance Methods boolean add (E o ); boolean addAll (Collection<? extends E> c ); void clear ( ); boolean contains (Object o ); boolean containsAll (Collection<?> c ); boolean equals (Object o ); int hashCode ( ); boolean isEmpty ( ); Iterator<E> iterator ( ); boolean remove (Object o ); boolean removeAll (Collection<?> c ); boolean retainAll (Collection<?> c ); int size ( ); Object[ ] toArray ( ); <T> T[ ] toArray (T[ ] a ); } ImplementationsAbstractSet , HashSet , LinkedHashSet , SortedSet Passed Tojava.security.cert.PKIXBuilderParameters.PKIXBuilderParameters( ) , java.security.cert.PKIXParameters.{PKIXParameters( ) , setInitialPolicies( ) , setTrustAnchors( )} , java.security.cert.X509CertSelector.{setExtendedKeyUsage( ) , setPolicy( )} , java.text.AttributedCharacterIterator.{getRunLimit( ) , getrunStart( )} , Collections.{checkedSet( ) , synchronizedSet( ) , unmodifiableSet( )} , javax.security.auth.Subject.Subject( ) Returned ByToo many methods to list. Type OfCollections.EMPTY_SET |