Using swt gem directly

use_swt.rb

#! /usr/bin/env jruby

require 'swt'

#module Swt
  #include_package 'org.eclipse.swt.graphics'
  #include_package 'org.eclipse.swt.events'
  #include_package 'org.eclipse.swt.dnd'

  #module Events
    #import org.eclipse.swt.events.PaintListener
    #import org.eclipse.swt.events.MouseMoveListener
  #end

  #module Widgets
    #import org.eclipse.swt.widgets.Canvas
  #end
#end

class SwtExample
  def initialize
    # A Display is the connection between SWT and the native GUI.
    display = Swt::Widgets::Display.get_current
    @shell = Swt::Widgets::Shell.new
    @shell.text = "Example"

    # A Shell must have a layout. FillLayout is the simplest.
    layout = Swt::Layout::FillLayout.new
    @shell.setLayout(layout)
    @shell.set_size 200, 200

    @shell.add_paint_listener do |event|
      event.gc.draw_text "Yo", 0, 0
    end

    # And this displays the Shell
    @shell.open
  end

  # This is the main gui event loop
  def start
    display = Swt::Widgets::Display.get_current

    # until the window (the Shell) has been closed
    while !@shell.isDisposed

      # check for and dispatch new gui events
      display.sleep unless display.read_and_dispatch
    end

    display.dispose
  end
end

Swt::Widgets::Display.set_app_name "Example"

app = SwtExample.new
app.start