Now that our sources are ready and builded, we want to run and debug the plugin. This is very easy, all you need is to open net.sf.j2s.core/plugin.xml and click the link "Launch an Eclipse application" or the link "Launch an Eclipse application in debug mode"
This will start a second Eclipse instance with our Java2Script plugin installed. Try to create a new Java2Script application and test your plugin's mdifications in that instance...
Like with any Eclipse plugin, rememeber that you can add breakpoints in Java code for better debbugging the Java to JavaScript compiler: