Is down casting considered bad practice?

Question

So, I have a set up like below where A and B are both abstract classes.

abstract class ObjectA extends ObjectB<ObjectC> {

}

public class ObjectD extends ObjectA{

    public static void main(String[] args){
        ObjectA x = new ObjectD();
        ObjectD y = (ObjectD)x; // down cast
    }

}

I'm using a library where I want to avail of the abstract methods in ObjectB and provide a default constructor for all classes - ObjectA. I'm not sure on my approach. BTW ObjectB is part of a predefine library I'm using. ObjectA is my own class providing default properties and constructor.

I'm not so sure on my approach, doesn't seem nice?

Just to add:

ObjectA requires a type that extends ObjectA.

public abstract class ObjectA<T extends ObjectA<T>> {

}

Hence, the need for what I'm doing.

Why not just declare the variable as the specific type in the first place? — chrylis -cautiouslyoptimistic-, Apr 09 '14 at 10:46
It's still not clear why you don't just declare `ObjectD xy = new ObjectD()` in place of the declarations of x and y. — Theodore Norvell, Apr 09 '14 at 11:58
@Thedore Norvell because I will have several different classes extending from ObjectD class. — user1543871, Apr 09 '14 at 13:05

score 2 · Answer 1 · answered Apr 09 '14 at 10:49

2

Note that in some cases you might get runtime error because by the explicit cast you're telling the compiler to trust you that you're not making errors, so it'll ignore the errors and won't detect it in compilation time.

As long as you know what you're doing, that's fine. To be safe, you can always use instanceof.

answered Apr 09 '14 at 10:49

Maroun

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Take a look at this post, also very helpful to suit your needs http://stackoverflow.com/questions/496928/what-is-the-difference-between-instanceof-and-class-isassignablefrom – Kenneth Clark Apr 09 '14 at 11:02

Is down casting considered bad practice?

1 Answers1