generics vs arrays

[Jeanne Boyarsky]

This code compiles and gives a runtime error:

ArrayList[] arrayList = new ArrayList[1];
Collection[] collectionArray = arrayList;
collectionArray[0] = new Vector(0);

This code gives a compiler error:

ArrayList<ArrayList> genericsArrayList = new ArrayList<ArrayList>();
Collection<Collection> genericsCollection = genericsArrayList;

I understand why the later doesn't compile - someone could add a Collection to genericsCollection which could not be stored in genericsArrayList. As far as I can tell, this is the same concept used in the array example - someone can store a vector in the collectionArray which arrayList cannot handle. I think these two examples are logically equivalent.

Are they different somehow? Is it that the array example is "legacied" in from Java 1.4 and doesn't get a compile time check?

[Jim Yingst]

[Jeanne]: Is it that the array example is "legacied" in from Java 1.4 and doesn't get a compile time check?

Yes, that's it. Basically Sun screwed up the original rules for array references, making them a bit too permissive on type checking in some circumstances. But they won't change that now for backward compatibility. Instead they just went ahead and used different rules for generics, and now encourage the use of generic collections in place of arrays.
[ April 23, 2008: Message edited by: Jim Yingst ]

[Jeanne Boyarsky]

Thanks Jim. Not only did you confirm my suspicions, but you added something i didn't even think to ask!

and now encourage the use of generic collections in place of arrays.