Re: dyamically loading class that implements an interface.
lambelly wrote:
On Jul 8, 8:49 am, Lew <l...@lewscanon.nospam> wrote:
lambelly wrote:
Thanks, I found the discussion you mentioned and through that was able
to infer what I was doing wrong. As I stated, I was trying to
call .newInstance() directly, which doesn't work in this instance. In
this instance I needed to create a java.lang.reflect.Constructor
first. I'm not sure if that's due to the interface or not. However,
you have helped solve a significant issue and I greatly appreciate
your assistance.
Please do not top-post (place your comments above the material to which you
are replying) but place your comments in line.
Sorry. In instances where I am not replying to a specific thing
someone said, but to the whole post in general I find top posting to
make the most sense. Perhaps I am wrong.
Your problem had nothing to do with the interface, nor do you ever need to
explicitly upcast (cast from a subtype to a supertype).
As Andrew said, an SSCCE (follow his link) would help, not only to explain the
question but to explain the answer. There potentially are many who would
benefit from your problem and its answer, but none of us can because you do
not tell us.
Originally, I was doing this -- note that I originally said "something
like this", but that this something is exactly what I was doing:
FileType fileType =
(FileType)
This cast is superfluous.
(Class.forName("fileuploadhandler.fileType.XmlFile").newInstance());
This invokes the parameterless (i.e., default) constructor only. You seem to
need a constructor that takes an argument.
Hard to tell since you never told us what the exception was.
This caused an instantiation error to be thrown. I figured that had to
/What/ error? I'll bet it was an Exception, not an Error. Which one? What
was the message? You keep hiding the facts.
do with my calling newInstance and newInstance not working on abstract
classes or interfaces. After I read Andrew's post and did more
research I changed the code to this:
Class fileTypeClass =
Class.forName("fileuploadhandler.fileType.XmlFile");
Constructor fileTypeConstructor = fileTypeClass.getConstructor (new
Class[] {String.class});
FileType ft = (FileType)fileTypeConstructor.newInstance("/path/to/
file");
which seems to work.
Proving that the problem was not instantiation of an interface, since that was
never what you were trying to do, but the fact that the parameterless
constructor either did not exist (most likely - hard to tell without the
exception information) or was the wrong one for your logic.
If you say "seems to work" because you aren't sure it does yet, then you need
more testing until you can aver that it does work. Understanding why you got
the error (ok, exception) will improve your certainty.
--
Lew