Re: usage of Java Channel Access Client

[Simon Rees via Tech-talk <tech-talk@aps.anl.gov>]

Dear all

Just a quick note on this discussion...

Thanks, Xuan, for putting this topic on our radar over here
at PSI. Also to Lewis for the documentation fixes that he
recently submitted to the library.

We will look at ways of improving the API and/or of making
sure that the README file offers more explicit guidance
for performing get/put bulk operations.

Best regards

Simon Rees
PSI Controls Developer


On 23.01.20 07:26, 吴煊 via Tech-talk wrote:
> Hi Lewis,
> Thanks for your reply. Could you give me an elegant way of example to call put method. It seems like that I need to create channel for 300 times by what you said.
> Cheers,
> Xuan
>
> 在 2020-01-23 06:01:00，"J. Lewis Muir" <jlmuir@imca-cat.org> 写道：
>
> > On 01/22, 吴煊 via Tech-talk wrote:
> > > My question is how to use each channel to put value? I've not found any example. I have tried: channels.get(0).put("test"), it's not correct.(error info:The method put(capture#1-of ?) in the type Channel<capture#1-of ?> is not applicable for the arguments (String))
> > That put method is just going to be awkward to use when the type of the
> > object it's called on is Channel<?> (i.e., a Channel of some type).
> > There are some other methods on Channel that you could call without
> > trouble, but put(T) will be problematic because its argument is of type
> > T and the object you're calling it on is a Channel of some type, not
> > necessarily type T.  If you have to call that method, the best you can
> > do is cast the Channel<?> object to the correct type, Channel<String> in
> > your example:
> >
> >   (Channel<String>(channels.get(0))).put("test");
> >
> > But that's ugly, and you're throwing away all of the benefits of
> > generics (e.g., type safety and expressiveness).  You'd also have to add
> > a @SuppressWarnings("unchecked") annotation to the method, or change
> > the code to a local variable assignment and put the annotation on the
> > variable, to get rid of the compiler warning.
> >
> > So, I'd say that you'd be better off not trying to call that put(T)
> > method like that.  Instead, stick to only calling methods on those
> > channels that you can call in a type-safe way.
> >
> > If you really need some way to do what you're trying to do, you'd
> > probably want something added to the ca API to help with that.
> >
> > If you have to do it yourself, though, you could create your own
> > container object that could hold Channel instances and that could
> > provide a get and put method that took a type token.  Then, assuming
> > "channels" was an instance of this container object, your example could
> > become something like this:
> >
> >   channels.put(0, String.class, "test");
> >
> > Of course, there are various designs you could come up with.
> >
> > Lewis