[jdom-interest] JDom and Java5

[Victor Toni]

Mattias Jiderhamn wrote:
> Rolf wrote (2008-02-27 17:19):
>> Mattias Jiderhamn wrote:
>>> Rolf wrote (2008-02-27 15:54):
>>>> Mattias Jiderhamn wrote:
>>>>> Rolf wrote (2008-02-27 02:55):
>>>>>> On the other hand, I think it would also be a *very good* 
>>>>>> solution to leave the method with a return type of List<?> 
>>>>>> because, as far as I can tell, it is fully compile-time 
>>>>>> backward-compatible with existing code,  ... I am sure would be 
>>>>>> far more receptive to migrate to 'JDom2' if the migration was 
>>>>>> 'seamless'.
>>>>> Does this mean you managed to compile
>>>>>  List<Elements> l = XPath.selectNodes(...)
>>>>> if XPath.selectNodes() returns List<?>; the case where I had to 
>>>>> add an explicit cast in comparison with the old raw "List" version 
>>>>> to avoid "incompatible types" error?
>>>>> How?
>>>>>
>>>> No, but this is what I can do...
>>>>
>>>> ...
>>>>
>>>> Now, the code following the above snippet is:
>>>>
>>>>        out.println("This WAR has "+ servlets.size() +" registered 
>>>> servlets:");
>>>>        Iterator i = servlets.iterator();
>>>>        while (i.hasNext()) {
>>>>            Element servlet = (Element) i.next();
>>>>            out.print("\t" + servlet.getChild("servlet-name")
>>>>                                    .getTextTrim() +
>>>>                      " for " + servlet.getChild("servlet-class")
>>>>                                       .getTextTrim());
>>>>            List initParams = servlet.getChildren("init-param");
>>>>            out.println(" (it has " + initParams.size() + " init 
>>>> params)");
>>>>        }
>>>>
>>>> The above construct is very typical of 'legacy' JDom and XPath usage.
>>>>
>>>> So, by returning List<?>, there are only compile-time warnings in 
>>>> existing legacy code, and the only difference between JDom1.1 and 
>>>> JDom2 is the details on the compiler warnings.
>>>
>>> Yes, but some of us have existing projects using Java5 and JDOM. In 
>>> some of those cases your port will - as far as I can understand - 
>>> NOT be "fully compile-time backward-compatible".
>>> I just want everybody to be fully aware of that.
>>>
>>> /Mattias
>>>
>>
>> Hmmm. that is a new angle on it, but, for the life of me, I can't 
>> think of any situation where it breaks things.... How could changing 
>> the return type from 'List' to 'List<?>' break any code? Returning 
>> List<Element> would surely break things though......
>
> See the (real life) example I have provided
>   List<Elements> l = XPath.selectNodes(...)
> gives a compiler warning with the current JDOM release, but does not 
> compile against your code.
>
> If we want a drop in replacement, I believe we will have to stick with 
> raw "List" for selectNodes().
>
> (It may also be worth noting that the main, or at least first, users 
> of JDOM with Java5 are probably those already on Java5 projects using 
> JDOM).
One could still use the mentioned "<T> List<T>" approach. This should 
work for old and new code without needing an explicit cast...