sjot.rb

require 'java'
java_import java.lang.System

Frame = javax.swing.JFrame
Button = javax.swing.JButton
Label = javax.swing.JLabel

frame = Frame.new("what")
button = Button.new("a button")
label = Label.new

button.add_action_listener do
  label.text = System.get_property('java.home')
end

frame.content_pane.layout = java.awt.FlowLayout.new
frame.content_pane.add(button)
frame.content_pane.add(label)

frame.set_default_close_operation(Frame::EXIT_ON_CLOSE)
frame.set_size(500, 100)
frame.visible = true