Java Reference
In-Depth Information
Listing 5-22 ' s main() method stores a 50MB LargeObject key and a String
value in the weak hashmap, and then removes the key's strong reference by assigning
null to lo . main() next enters a while loop that executes until the map is empty
( map.isEmpty() returns true).
Each loop iteration begins with a System.gc() method call, which may or may
garbagecollection,theiterationthencreatesa LargeObject objectandthrowsaway
move the map's solitary entry.
When I run this application on my Windows XP platform, I observe the following
finite loop:
{LargeObject@5224ee=Large Object}
Note WeakHashMap is useful for avoiding memory leaks, as explained in Brian
ences” (
p11225/ ).
The EnumMap class provides a Map implementation whose keys are the members of
the same enum. Null keys are not permitted; any attempt to store a null key results in
athrown NullPointerException .Becauseanenummapisrepresentedinternally
as an array, an enum map approaches an array in terms of performance.
EnumMap supplies the following constructors:
EnumMap(Class<K> keyType) createsanemptyenummapwiththespe-
cified keyType . This constructor throws NullPointerException when
keyType contains the null reference.
EnumMap(EnumMap<K,? extends V> m) createsanenummapwiththe
samekeytypeas m ,andwith m 'sentries.Thisconstructorthrows NullPoint-
erException when m contains the null reference.
Search WWH ::

Custom Search