On OSX, if the line of text supplied to contentText is too wide for an Alert dialog, the text wraps indefinitely.
On linux, if the line of text supplied to contentText has a whitespace character and the remaining text is a large token, ellipses are shown.

A minimal test case to reproduce:

{noformat}
java_import 'javafx.scene.control.Alert'
require 'jrubyfx'

class OverrunInconsistency < JRubyFX::Application
  def start(stage)
    with(stage, width: 1000, height: 1000, title: 'Hello JRubyFX') do
      layout_scene do
        alert = Alert.new(Alert::AlertType::ERROR)
        alert.title = 'Alert'
        alert.header_text = 'header'
        alert.content_text = "OSX will wrap, linux will ellipses: " + "#{__FILE__}" * 30
        alert.show_and_wait
      end
      show
    end
  end
end

OverrunInconsistency.launch
{noformat}

This is jruby, but I'm fairly confident this issue will exist in plain java land.