Set implementation for use with enum types. All of
the elements in an enum set must come from a single enum type that is
specified, explicitly or implicitly, when the set is created. Enum sets
are represented internally as bit vectors. This representation is
extremely compact and efficient. The space and time performance of this
class should be good enough to allow its use as a high-quality, typesafe
alternative to traditional int-based "bit flags." Even bulk
operations (such as containsAll and retainAll) should
run very quickly if their argument is also an enum set.
The iterator returned by the iterator method traverses the
elements in their natural order (the order in which the enum
constants are declared). The returned iterator is weakly
consistent: it will never throw
and it may or may not show the effects of any modifications to the set that
occur while the iteration is in progress.
Null elements are not permitted. Attempts to insert a null element
NullPointerException. Attempts to test for the
presence of a null element or to remove one will, however, function
Like most collection implementations, EnumSet is not
synchronized. If multiple threads access an enum set concurrently, and at
least one of the threads modifies the set, it should be synchronized
externally. This is typically accomplished by synchronizing on some
object that naturally encapsulates the enum set. If no such object exists,
the set should be "wrapped" using the
method. This is best done at creation time, to prevent accidental
Set<MyEnum> s = Collections.synchronizedSet(EnumSet.noneOf(MyEnum.class));
Implementation note: All basic operations execute in constant time.
They are likely (though not guaranteed) to be much faster than their
HashSet counterparts. Even bulk operations execute in
constant time if their argument is also an enum set.
This class is a member of the Java Collections Framework.