Java Reflection

Some people think java reflection is cool (they are mistaken, it is not is a pain), where possible avoid using it at all costs, unfortunately some of the processing guys seem to think it is cool, so they have contaminated the processing api with it. Fortunately there are often ways to avoid it (and sometimes come up with something that is more appropriate for use in a ruby environment). One such example is the thread convenience method of processing, that relies on reflection to allow you to pass a function to a thread.

thread("someFunction");
void someFunction(){
  do stuff..
}

In ruby-processing we have overridden the thread convenience method to be much more ruby like (in keeping with ruby Thread, whilst actually using a java thread under hood) to take a block.

thread do
  some stuff..
end

Actually we don't really need this convenience function in ruby-processing we've just overridden it to prevent any confusion, it is just as easy to use the existing Thread syntax...

Thread.new do
  some stuff..
end

Another example where reflection gets pressed into action is the recommended way that you "registerMethods" with the processing Applet from a processing library, this is done using reflection as follows

public BasicLibrary(PApplet parent) {
    this.parent = parent;
    parent.registerMethod("dispose", this);
  }

  public void dispose() {
    // Anything in here will be called automatically when 
    // the parent sketch shuts down. For instance, this might
    // shut down a thread used by this library.
  }

You have to go through hoops to replicate this in ruby but it can be done:-

require 'jruby/core_ext'

class TestRegister
  attr_reader :parent
  def initialize parent
    @parent = parent
    register = parent.java_method :registerMethod, [Java::JavaLang::String, java.lang.Object]
    register.call(:draw, self)
    register.call(:pre, self)
  end

  def pre
    puts "before draw"
    parent.background(100)
  end

  def draw
    puts "at begin draw"
    parent.fill(200, 100)
    parent.ellipse(100, 100, 60, 60)
  end


end

cls = TestRegister.become_java!

The magic in the last line ensures that the TestRegister class becomes java, so that when you pass self, it is a java.lang.Object. And believe it or not this actually works see following sketch:-

load "./register.rb"

def setup
  size 200, 200
  fred = TestRegister.new self
  no_loop
end

def draw
  fill(0, 0, 200)
  ellipse(120, 120, 60, 60)
end

Anyone who can get registerMethod("MouseEvent") or registerMethod("KeyEvent") to actually work in ruby-processing might find this useful, also please report how you got it to work!!!