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Java Forum / General / November 2005Does Class casting survive an ObjectStream
Lets say I create a Vector that has class cast of holding Strings. I then store that Vector to disk via ObjectStreams and FileStreams. When I retrieve the Vector later. Will the Class casting survive the storage process? I know I could do an experiment to find this out, but I am also looking for resoning behind the behaviour of the language. Thanks for any help you can give in this matter. > Lets say I create a Vector that has class cast of holding Strings. I > then store that Vector to disk via ObjectStreams and FileStreams. [quoted text clipped - 6 lines] > > Thanks for any help you can give in this matter. Realize that casting doesn't actually change the type of any objects, so the objects you insert into the vector continue to be whatever they were before you inserted them. Your vector will contain the same kinds of objects after reconstruction as it did before. /gordon  Signature[ do not email me copies of your followups ] g o r d o n + n e w s @ b a l d e r 1 3 . s e > Lets say I create a Vector that has class cast of holding Strings. I then > store that Vector to disk via ObjectStreams and FileStreams. [quoted text clipped - 8 lines] > > Thanks for any help you can give in this matter. If the question is "What do I get when I serialize a Vector<String>", the answer is "A Vector".You can deserialize it back into a Vector, Vector<Object>, Vector<String>, or even Vector<Integer>, though in the last case you'll generate a lot of ClassCastExceptions trying to get objects from it.. This has to do with the notion of erasure: at runtime, the type variables are erased, and a collection, unlike an array, has no idea what type it was declared to contain. I am afraid you have answered the wrong question. I will try to be a little clearer. I am aware that if I put a Vector in full of strings, i will get back a Vector full of Strings. What I am after is: If I try to add an int to this Vector after I have retrieved it what will happen? >I am afraid you have answered the wrong question. > [quoted text clipped - 5 lines] > What I am after is: If I try to add an int to this Vector after I have > retrieved it what will happen? That's not it, since you can't add a scalar to a Vector regardless. I will assume you means "add an Integer". If you've retrieved it into a Vector<String> you'll get a compilation error. If into a Vector ot Vector<Object>, it'll work fine. As I said earlier, Collections are unlike arrays: they don't know what type they're supposed to contain. >That's not it, since you can't add a scalar to a Vector regardless. Ok, That was a silly mistake to make... >I will assume you means "add an Integer". If you've retrieved it into a >Vector<String> you'll get a compilation error. If into a Vector ot >Vector<Object>, it'll work fine. As I said earlier, Collections are unlike >arrays: they don't know what type they're supposed to contain. This is what I am after. Thanks. Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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