Java coding style, local variables vs repeated method calls

Question

I prefer to use local variables rather than multiple calls to the same method.

/*
 * I prefer this
 */
Vehicle vehicle = person.getVehicle()
if (vehicle instanceof Car) {
   Car car = (Car) vehicle;
   car.openSunroof();
} else if (vehicle instanceof Bike) {
   Bike bike = (Bike) vehicle;
   bike.foldKickstand();
}
/*
 * Rather than this
 */
if (person.getVehicle() instanceof Car) {
   Car car = (Car) person.getVehicle();
   car.openSunroof();
} else if (person.getVehicle() instanceof Bike) {
   Bike bike = (Bike) person.getVehicle();
   bike.foldKickstand();
}

• I believe that the first way is going to perform a tiny bit faster
• I think the second way violates the DRY principle
• I find the first way more readable and easier to debug (... OK negligible because I could step over)
• I don't want to have to deal with the possibility of changed object state

Which do you prefer and why?

Answer 1

I prefer the first version for all the reasons you've mentioned. In particular (just to spell out your fourth point), it means you're definitely going to get consistent results... you could get horribly nasty results with the second version if getVehicle() returned a Car on the first call, then a Bike on the second...

The performance side doesn't bother me (I'll happily call List.size() repeatedly, for example) but readability, consistency and non-repeating are all much more important. Essentially the first snippet conveys the idea of "get a value, then use it" much more effectively than the second does.

So yes, I'm with you... is anyone recommending the second form to you?

Answer 2

Yeah the first one is definitely better. I would never go for the second method. But you should think of using polymorphism more. Relying on instanceof so heavyly is not good OO design.