Java Reference
In-Depth Information
ation nodes) and disk sectors. And bitsets are useful in
Huffman coding
, a data-com-
pression algorithm for achieving lossless data compression.
Creating Your Own Collections
Arrays,theCollectionsFramework,andlegacyclassessuchas
BitSet
aresuitablefor
organizinggroupsofobjects(or,inthecaseof
BitSet
,setsofbitsthatareinterpreted
asBooleantrue/falsevalues),andyoushouldusethemwhereverpossiblebeforecreat-
ing your own collection APIs. After all, why “reinvent the wheel?”
The Collections Framework supports lists, sets, queues, deques, and maps. If your
collectionrequirementcanfitintooneofthesecategories,thengowiththisframework.
Keepinmindthatyoucanalsotakeadvantageoftreesin
TreeSet
and
TreeMap
im-
plementation contexts, and stacks in deque contexts.
Perhaps you need a different implementation of one of the Collections Framework
core interfaces. If so, you can extend this framework by implementing the interface,
or by subclassing one of the more convenient “
Abstract
” classes, such as
Ab-
stractQueue
. For example, author Cay Horstmann demonstrates extending this
classtoimplementacirculararrayqueue(see
http://www.java2s.com/Code/
OBEYING CONTRACTS
Whenyouimplementacoreinterfaceorextendoneofthe
Abstract
classes,you
should ensure that your implementation class doesn't deviate from the various con-
tracts described in the Java documentation for these interfaces. For example,
List
places the following stipulation on the
hashCode()
method that it inherits from
Collection
:
The hash code of a list is defined to be the result of the following calculation:
int hashCode = 1;
for (E e: list)
hashCode = 31*hashCode+(e==null ? 0 : e.hashCode());
This calculation ensures that
list1.equals(list2)
implies that
list1.hashCode() == list2.hashCode()
for any two lists,
list1
and
list2
, as required by the general contract of
Object.hashCode()
.
