title: Java Event Listener to detect a variable change
body: <p>I cannot seem to find an answer anywhere to my question. Is there any event listener which can detect the changing of a boolean or other variable and then act on it.  Or is it possible to create a custom event listener to detect this? </p>
  
  <p>Please I cannot seem to find a solution to this anywhere and I found <a href="http://www.exampledepot.com/egs/java.util/CustEvent.html">this website</a> explaining how to create custom events</p>