Enum maps are maintained in the natural order of their keys
(the order in which the enum constants are declared). This is reflected
in the iterators returned by the collections views ( keySet() ,
entrySet() , and values() ).
Iterators returned by the collection views are weakly consistent:
they will never throw ConcurrentModificationException and they may
or may not show the effects of any modifications to the map that occur while
the iteration is in progress.
Null keys are not permitted. Attempts to insert a null key will
throw NullPointerException . Attempts to test for the
presence of a null key or to remove one will, however, function properly.
Null values are permitted.
Like most collection implementations EnumMap is not
synchronized. If multiple threads access an enum map concurrently, and at
least one of the threads modifies the map, it should be synchronized
externally. This is typically accomplished by synchronizing on some
object that naturally encapsulates the enum map. If no such object exists,
the map should be "wrapped" using the synchronizedMap(Map)
method. This is best done at creation time, to prevent accidental
Map<EnumKey, V> m
= Collections.synchronizedMap(new EnumMap<EnumKey, V>(...));
Implementation note: All basic operations execute in constant time.
They are likely (though not guaranteed) to be faster than their
This class is a member of the
Java Collections Framework.