3

I'd like to define a superclass in Java, then define a subclass in Ruby, then make instances of that subclass in Java. A little something like this:

// Java superclass
package myPkg;

public class Sup{
  public Sup(){}
  public abstract void foo(String a);
}

--

# Ruby code
include Java
require 'jruby/core_ext'

include_class 'myPkg.Sup'

class RubySub < Java::myPkg.Sup
  def foo( a )
    puts a;
  end
end

RubySub.become_java!
RubySub

--

// Back in Java land
Ruby runtime =  Ruby.newInstance();
IRubyObect ro = runtime.evalScriptlet(theRubyCodeAbove);
Class<Sup> clz = (Class<Sup>) JavaEmbedUtils.rubyToJava(runtime, ro, Class.class);
clz.newInstance().foo("Hey!");

I've tried the above code, but I get an InstantiationException from the newInstance() call. I want to have the class declared in Ruby at runtime, so e.g. running jrubyc to compile the Ruby code to a Java class definition ahead of time is out. What am I doing wrong here?

I've run through the bottom code segment in the debugger, and I'm definitely getting a RubyClass object returned from the evalScriptlet() call. Maybe there's an extra step involved to turn a RubyClass into a Class?

UPDATE: I have a lead -- apparently become_java! doesn't work if the class is a subclass of a Java class. Is there another way I can do this, or am I just boned?

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I've come up with a workaround for now, but it's not pretty.

In brief: I can't return RubySub.become_java! (which is nil, because of JRUBY-6105) or try to return RubySub and convert from a RubyClass to a Class.

Instead, I return RubySub.method(:new), which shows up as a RubyMethod. I can call this, and it creates an IRubyObject which is actually an instance of the subclass. This can be cast to the Java superclass using JavaEmbedUtils.rubyToJava(). Like I said, it's not pretty but it works.

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4 Comments

Interesting... I was referred to your question from my own In my case, I tried your above solution with a class that inherits from VBox (javafx): class Controller < Java::javafx.scene.layout.VBox; end With no luck: #<NameError: no method 'rubyToJava' for arguments (org.jruby.proxy.javafx.scene.layout.VBox$Proxy2) on Java::OrgJrubyJavasupport::JavaEmbedUtils>
The rubyToJava call that I'm making takes 3 arguments -- the runtime (Ruby) instance, the object (IRubyObject), and the target (i.e. Java parent) class. Yours would look like JavaEmbedUtils.rubyToJava(myRubyInterp, theController, VBox.class). I read your question, and it's a shame that framework code is outside your control. Calling getDelcaredMethods() is a terrible, un-ruby-ish way to solve the problem, when they should have used respond_to?.
The third party in this case is java code (which I have no affiliation with, or command of), which is using reflection to see all functions defined in the (now) java-ized version of my class. So in this case what I was hoping for was that ruby methods would automatically be seen in the java-ized version of the code and could be called from the java class. This sounds like it might be a different than what you're trying to do above. Either way I was hoping become_java would do it, like you have it here, but it seems as though it does not.
A quick aside: I had also tried java_signature to do this, but that seems like it has no effect. I'm not sure if it's related to the become_java issue or not... it looks as though there have been other java_signature issues, referenced here. I'm also probably outside of the scope of your post now as well - if so my apologies.

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