Swing generification changes in JDK 9 b24 -- swing generification refinements in JDK 9 b30

[Andrej Golovnin]

Hi Joe,

I have tested JDK 9b30 with my project and I still have compile errors. I
have a code which looks like this:

class BeanNode extends DefaultMutableTreeNode {
 ...
}

@SuppressWarnings("unchecked")
private void aMethod() {
    BeanNode node = ....
    ....
    Enumeration<BeanNode> children = node.children();
    ...
}

The compiler reports for this code following error:

error: incompatible types: Enumeration<TreeNode> cannot be converted to
Enumeration<BeanNode>

because the DefaultMutableTreeNode defines the method #children() as:

public Enumeration<TreeNode> children() {
   ...
}

Best regards,
Andrej Golovnin

On Wed, Sep 17, 2014 at 6:11 AM, Joe Darcy <joe.darcy at oracle.com> wrote:

> Hello swing developers,
>
> In response to the earlier call for feedback on the initial swing
> generification changes, several bugs were filed and fixed:
>
>     JDK-8054360: Refine generification of javax.swing
>     https://bugs.openjdk.java.net/browse/JDK-8054360
>
>     JDK-8055254: Address source incompatability of JSlider generification
>     https://bugs.openjdk.java.net/browse/JDK-8055254
>
> These fixes are now present in JDK 9 b30:
>
>     https://jdk9.java.net/download/
>
> Please give b30 a try when recompiling your favorite swing code base and
> report on how the refined generification works.
>
> Thanks,
>
> -Joe
>
> On 8/5/2014 9:25 AM, Joe Darcy wrote:
>
>> Hello,
>>
>> A quick follow-up, I've filed
>>
>>     JDK-8054360: Refine generification of javax.swing
>> https://bugs.openjdk.java.net/browse/JDK-8054360#comment-13532821
>>
>> to tweak the generification of TreeNode and possibly a few other types.
>>
>> Thanks for the feedback,
>>
>> -Joe
>>
>> On 7/30/2014 7:54 AM, Joe Darcy wrote:
>>
>>> Hi Andrej and Martijn,
>>>
>>> Thanks for responding.
>>>
>>> On 7/28/2014 5:04 AM, Andrej Golovnin wrote:
>>>
>>>> Hi Joe,
>>>>
>>>> I'm not sure if it is what you are looking for.
>>>>
>>>
>>> For context, the general evolution policy of the JDK:
>>>
>>> http://cr.openjdk.java.net/~darcy/OpenJdkDevGuide/
>>> OpenJdkDevelopersGuide.v0.777.html#general_evolution_policy
>>>
>>> includes "avoid introducing source incompatibilities." As this is a
>>> large generification change to swing, some level of source incompatibility
>>> may be acceptable in a platform release like JDK 9, but if there are very
>>> widespread issues, some of the changes may be reconsidered.
>>>
>>> The request to try out the changes was to get enough information to see
>>> if any (partial) reconsideration was warranted.
>>>
>>>
>>>  But I tried to compile my project with the new build. And I got a
>>>> compile error in one of my classes. I have a class which implements the
>>>> TreeNode interface and looks like this:
>>>>
>>>> class MyTreeNode implements TreeNode {
>>>> ....
>>>>     @Override
>>>>     public Enumeration<MyTreeNode> children() {
>>>>         return ....;
>>>>     }
>>>> ...
>>>> }
>>>>
>>>> The error message is: "return type Enumeration<MyTreeNode> is not
>>>> compatible with Enumeration<TreeNode>".
>>>>
>>>> If I change (see attached patch) the definition of the
>>>> children()-method in the TreeNode-interface to:
>>>>
>>>> public interface TreeNode {
>>>> ...
>>>>     Enumeration<? extends TreeNode> children();
>>>> ...
>>>> }
>>>>
>>>> then my code compiles.
>>>>
>>>
>>> That design issue was raised during code review:
>>>
>>> http://mail.openjdk.java.net/pipermail/swing-dev/2014-June/003643.html
>>>
>>> "It was not immediately clear how javax.swing.tree.TreeNode.children(),
>>> which returns a raw Enumeration, should be generified. I changed it to
>>>
>>>      Enumeration<TreeNode> children();
>>>
>>> and that seems to work fine. Something like
>>>
>>>      Enumeration<? extends TreeNode>
>>>
>>> with a covariant override would save a few casts in a private
>>> implementation, but generally doesn't seem to be a good trade-off since
>>> many normal clients could be inconvenienced dealing with the wildcard."
>>>
>>> If generified subclasses of TreeNode are common, the generification of
>>> children may need reconsideration.
>>>
>>>
>>>> BTW, a good test for your changes would be to try to compile NetBeans
>>>> and/or IntelliJ IDEA using the new JDK 9 build. They both are really big
>>>> Swing applications which make use maybe of all Swing APIs.
>>>>
>>>>
>>>>
>>> My preference would be for the NetBeans and IntelliJ teams to do that
>>> task :-)
>>>
>>> Thanks,
>>>
>>> -Joe
>>>
>>
>>
>