title: Adding a Listener to a StringWriter
body: <p>I have a class that creates <code>StringWriter</code>s and passes them around. A calling class will write to that Writer. Is there any way for me to put some sort of Listener on the Writers as they are being created to let me know when their contents change?</p>
  
  <p>I tried looking online, but all I could find about Listeners were for GUIs, and this is not GUI-related.</p>