From http://lists.bluej.org/pipermail/bluej-discuss/2005-February/004503.html
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The appletwn.jar is not set up to be able to be used as a custom class library. I have uploaded a modified version which can be used this way, and which incorporates a few improvements: http://www.bluej.org/resources/classes/appletwn2.jar Also I have written the following notes on how to use it. Please note, you can either put the jar file in C:\BlueJ\lib\userlib OR in add it into the list in Tools/Preferences/Libraries. There's no need to do both. Davin AppletWindow provides a Java window that can display an applet. This environment allows you to use BlueJ's symbolic debugger to debug your applet code. Author: Michael Trigoboff EMail: mltsoftware at attbi.com Web: http://mltsoftware.home.attbi.com Modified by: Davin McCall, 24/02/2005 Email: davmac at bluej.org How to use AppletWindow ----------------------- First download the appletwn.jar file, which contains all the relevant classes and source code. You can use appletwn.jar as a custom class library as detailed at: http://www.bluej.org/help/archive.html#tip5 To run your applet, do the following: 1) Set any breakpoints that you require 2) Instantiate your applet onto the object bench. Call it "applet" (for example). 3) Instantiate the AppletWindow class. The constructor takes four parameters: the window title, the width and height, and the applet. You can instantiate AppletWindow by using "Use Library Class" from the tools menu. Type in the name of the class (AppletWindow) and press Enter, then double click on the constructor. See the BlueJ reference manual for more information. In BlueJ 2.0+, you can also use the code pad: new AppletWindow("title", 200, 200, applet1) That's it! A window will appear, your applet contained within. Other hints ----------- * You can see the full source code for AppletWindow by extracting the contents of the appletwn.jar file. * It's possible to supply parameters for the applet using the AppletParams class. Put an instance of this class on the bench and use the "setParam" method to set parameter values. Then use the five-argument version of the AppletWindow constructor and give the AppletParams instance as the fifth parameter. * See a demo of the AppletWindow by calling the static method "execute" (with no parameters) in the AppletDemo class. There is also an execute method taking a String parameter, which can be used to set the text appearing inside the demo applet.