Hi Donny,
Thanks for the explanation, but the types might be a red herring. I'm
less concerned about that than the fact that Tapestry seems to be
assigning one of my variables to a different variable. It doesn't
matter if the types are the same or different. I could've had:
@SessionState(create=false)
private List<String> list1;
@SessionState(create=false)
private List<String> list2;
And I'd still expect to have two separate/distinct variables and
lists, not two variables pointing to the same list (unless I
specifically assigned them to the same list myself).
Thanks,
mrg
On Thu, Jan 6, 2011 at 9:57 AM, Donny Nadolny <donny.nado...@gmail.com> wrote:
> Your two lists are the same - they're both of type List so they both get
> assigned to the same thing. See below for why.
>
> The solution is to make two classes, one that holds the booleans, and one
> that holds the strings. Technically you would only need to do that for one,
> but it's probably a good idea to do it for both anyway.
>
> The reason why they're both considered the same: this has to do with how
> generics work in Java. It's called type erasure - after the class is
> compiled, the generic type is erased, so at runtime it doesn't care what the
> type is. Generics are a compile time check.
>
> For example, you could do:
> List<String> strings = new ArrayList<String>();
> List strings2 = strings;
> strings2.add(new Object()); //this line is fine
> String string = strings.get(0); //throws ClassCastException
>
> You might think that the strings2.add(new Object()) would have a problem
> because strings2 is pointing to strings which is an ArrayList<String>, but
> it doesn't because at runtime it doesn't do any checks, or even know that
> you put <String> there (well, there's certain ways of figuring it out, but
> generally just accept that it doesn't know). All it can do is give a warning
> at "List strings2 = strings" because you're doing some potentially type
> unsafe things.
>
>
> On Thu, Jan 6, 2011 at 9:38 AM, Michael Gentry <mgen...@masslight.net>wrote:
>
>> Hi everyone,
>>
>> Given the following page class:
>>
>>
>> public class Bug
>> {
>> �...@inject
>> private Logger log;
>>
>> �...@sessionstate(create=false)
>> private List<Boolean> booleans;
>>
>> �...@sessionstate(create=false)
>> private List<String> strings;
>>
>> void onActivate()
>> {
>> log.debug("booleans = " + booleans);
>> log.debug("strings = " + strings);
>>
>> if (booleans == null)
>> booleans = new ArrayList<Boolean>();
>>
>> booleans.add(Boolean.TRUE);
>>
>> log.debug("booleans: " + booleans);
>> log.debug("strings: " + strings);
>> log.debug("equal? " + booleans.equals(strings));
>> }
>> }
>>
>> I get this output:
>>
>> DEBUG 2011-01-06 09:35:24,014 booleans = null
>> DEBUG 2011-01-06 09:35:24,014 strings = null
>> DEBUG 2011-01-06 09:35:24,014 booleans: [true]
>> DEBUG 2011-01-06 09:35:24,014 strings: [true]
>> DEBUG 2011-01-06 09:35:24,015 equal? true
>>
>>
>> Even though I don't add anything to the strings list or even allocate
>> the strings list, it seems to be pointing to the booleans list, which
>> is, of course, incorrect. This seems to be happening on both 5.1 and
>> 5.2. Am I missing something?
>>
>> Thanks,
>>
>> mrg
>>
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