Re: Abstract class or interface?
- From: ozbear@xxxxxxxxxxx (ozbear)
- Date: Tue, 03 May 2005 11:00:34 GMT
On Sun, 1 May 2005 19:35:19 -0400, "Brett" <no@xxxxxxxx> wrote:
>I'm still trying to figure out concrete reasons to use one over the other.
>I understand the abstract class can have implementation in its methods and
>derived classes can only inherit one abstract class. The interface has
>implied abstract methods/properties and derived classes can inherit multiple
>interfaces. The interface properties/methods have no implementation.
>
>Besides definitions of the two, what are some conceptual reasons to use one
>over the other? Perhaps examples of this project uses an abstract classes
>vs. this one uses an interface...for these reasons.
>
>I have one project that uses an interface. I chose the interface over an
>abstract class because the derived classes all do the same thing, they just
>go about doing it in slightly different ways. Their results are different
>but conceptually what they do is the same thing. I don't ever see the need
>for adding more methods or properties to the interface. If there is every
>such a need, I can encapsulate this variability into one of the derived
>classes, since it will be "one" that has such a need rather than all. That
>make sense?
>
>Thanks,
>Brett
I have a 3-D package that under user control needs to be able to move
and rotate "things" along all three X, Y, and Z coordinate axis.
The "things" could be sinple points (Vertex class), lines (Line
class), planar faces (Faces class), or solid things (Solids class).
All these things are defined as supporting the I3D interface whch
means they must implement methods such as Rotate(x angle, y angle,
z angle), Translate(some axis), Scale(some percentage), and so forth.
Rotating a Vertex is different than a Line, but the interface doesn't
know nor care what the differences are. Furthermore, I can place all
the different things in an ArrayList by their interface and then run
a simple...
foreach (I3D i3dobj in arraylist)
i3dobj.Rotate(xangle,yangle,zangle);
to rotate all the objects in the scene.
In this example it would be possible to define an abstract class
called, say, Ab3D, and have Vertex, Line, Face, etc., derive from
Ab3D and override the Rotate, Translate, etc. methods in each.
THis implies some closer coupling between these classes than I
would like, furthermore...
What if I want to include rotated text or something else where
the bulk of the work is already defined in an existing class which
does not derive from Ab3D? If I don't have control of that existing
class' definition, or if it itself is a derived class I cannot make it
derive from Ab3D to override those methods.
With interfaces however, I can derive a new class from that already
existing one, state that it supports the I3D interface, and then
write the supporting Rotate, Translate, etc., methods for it. Then I
can include it in the arraylist above and perform the 3D actions on
it with no changes to manipulation code. I do not have to change
the interface to make new things 3D manipulatable.
Oz
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