[armedbear-devel] anonymous inner class in abcl

[Alessio Stalla]

On Tue, Aug 16, 2011 at 10:27 PM, Patrice Seyed <apseyed at gmail.com> wrote:
> Right,
>
> Hello abcl developers,
> Let's say I want to implement an anonymous inner class, just for example
> ActionListener with method actionPerformed:
> JButton button = new JButton("Enter");
> button.addActionListener(new ActionListener (){
> public void actionPerformed(ActionEvent e){
>
> System.out.println("The Enter button was pressed");
> }
> });
> What is the best way to do this in abcl?

Hi Patrice,

Welcome to the ABCL list!
"implementing an anonymous inner class" is ambiguous: when in Java you
write an inner class, you do so to implement an interface or to extend
another class. Inner classes are only a Java-the-language (javac)
construct, but for the JVM they're classes like any others. So, your
question should be: how do I implement an interface (like
ActionListener) in ABCL? How do I extend a class (like MouseAdapter)
in ABCL?
For the first question, there are two operators: jmake-proxy and
jinterface-implementation. The first is newer and more powerful but
less documented. You can find both of them in the file java.lisp in
ABCL's sources. For the simple case of interfaces with a single method
(SAM - single abstract method) you can do like this (untested):
(jmake-proxy "java.awt.event.ActionListener" (lambda (obj method
event) (declare (ignore obj method)) (handle-my-event event)))

For the second question, there's currently no way to define new Java
classes in Lisp. Technically it's doable and not particularly hard,
but nobody did it yet. (ABCL used to support it long time ago). I was
supposed to look into it some time ago but never found the actual time
for doing it.

Hope that answers your question - if not, do not hesitate to write back!

Cheers,
Alessio