Thanks for your comprehensive answer! I see now that using the base
features makes it easier to modify which implementation is used at later
stage. I will bear this in mind in the future.
Regards,
Fred.
On 01/08/2012 01:59 AM, Mihai DINCA wrote:
Hi Fred
You have put your finger on a basic feature - important to understand.
You need a class performing a specific task (in your case you need
something that behaves like a Set). There are several way to implement
the overall behavior, but not all the ways are the most efficient for
all the use case.
Let's take another (hypothetical) example: you wish to provide some
classes performing Complex number arithmetic. Inside your Complex
class you may store the Real part and the Imaginary part as two double
values. Or you may store the modulus and the angle (as two double
values too). In the first case additions would be faster. In the
second case multiplications would be faster.
Your library class may be use in programs who perform mainly additions
or in programs who perform mainly multiplications. What to do to
always provide the best response times?
A solution is to provide a "ComplexNumber" interface, then to create
two classes implementing it: "CNumbersForAddition" and
"CNumbersForMultiply".
The "end user" of your library would write his/her program using as
much as possible the interface. Such as "ComplexNumber c = new
CNumbersForAdition();". Then he/she would run a test and see how fast
it performs. Then replace all the "new" statements such as
"ComplexNumber c = CNumbersForMultiply();" and compare the response
times.
In the same way, it is a good idea to use "Set s = new HashSet();" and
use only the "Set" features. If you find at a later moment that
another set implementation is better for your case, you can easier
modify everything later.
Of course, there is an exception: if you absolutely need the HashSet()
supplementary features (that are not implementations of the Set
interface methods).
Hope it Helps
Michel Mihai Dinca
On 05/01/2012 22:42, Friedrich Clausen wrote:
Hello,
In section 1.2, in exercise program Set-HashSet-FindDup we declare a
new HashSet like so -
Set s = new HashSet();
but I notice that
HashSet s = new HashSet();
also works. What is the recommended way to create a new HashSet
instance?
Thanks!
Fred.
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