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The example is inflexible because it hardwires the ArrayList class into multiple
locations. This hardwiring focuses the developer into thinking specifically about array
lists instead of generically about lists.
issuebroughtaboutby profiling (analyzingarunningapplicationtocheckitsperform-
ance), suggests that the developer should have used LinkedList .
needtochange ArrayList to LinkedList ,tosatisfythecompiler,considerchan-
ging arrayList to linkedList , to keep semantics (meaning) clear—you might
have to change multiple occurrences of names that refer to an ArrayList instance
throughout the source code.
The developer is bound to lose time while refactoring the code to adapt to
LinkedList . Instead, the developer could have saved time by writing this example
torelyoninterfaces,andtoonlyspecify ArrayList inoneplace.Thefollowingex-
ample shows you what the resulting code would look like:
List<String> list = new ArrayList<String>();
void dump(List<String> list)
// suitable code to dump out the list
profiling change suggests that LinkedList should be used instead of ArrayList ,
simplyreplace Array with Linked andyouaredone.Youdonotevenhavetochange
the parameter name.
Javaprovidesinterfacesandabstractclassesfordescribing abstract types (typesthat
cannot be instantiated). Abstract types represent abstract concepts (drawable and
shape, for example), and instances of such types would be meaningless.
Interfaces promote flexibility through lack of implementation— Drawable and
List illustratethisflexibility.Theyarenottiedtoanysingleclasshierarchy,butcan
be implemented by any class in any hierarchy.
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