Matlab / Java API callback

Question

I'm designing an API (in Java) and expect to have users accessing the API from Matlab. The problem is that I want the API to provide a piece of functionality like:

javaApi.waitUntilPredicateIsTrue(Predicate<JavaObj> test);

My API (in the background) gets hold of instances of Java Obj (via some mechanism, e.g. polling). I want this API method to block until one of these instances, when passed to the Predicate evaluates to true. If I was calling this API from Java, I'd do:

javaApi.waitUntilPredicateIsTrue(new Predicate<JavaObj>() {
    public boolean evaluate(JavaObj jo) {
        return "READY".equals(jo.getState());
    }
});

You get the idea.

How can this be called from within Matlab? Can I use anonymous inner classes from Matlab? Can I declare a Matlab classdef which extends the interface Predicate (can this cope with the Java generic version)?

Answer 1

Matlab has a much nicer solution than forcing users to create a whole class just to provide a single method. Take a look at their anonymous functions.

Note that anonymous functions in Matlab have odd scoping rules. Make sure you read the "Variables Used in the Expression" section of the linked help page. If you want more traditional lexical scoping, take a look at nested functions.

EDIT: I am assuming that you will be doing the polling from Matlab, not passing the predicate function to Java. Example:

function waitForPredicate(pred)
  while pred
  end
end

waitForPredicate(@()javaApi.isMyConditionMet());

Answer 2

That sounds like a tough question. I'm still running R2006b so this may have changed, but it looks like MATLAB will not translate function handles (incl. anonymous functions) and structures into Java objects. I don't know about MATLAB custom classes, since the syntax has changed. Strings, arrays, and cell arrays will translate properly. They don't comment at all on implementing interfaces. (:p :p :p BOO HISS)

edit: just found this page on Matlab Central, it talks about some undocumented interfaces.