JFormDeveloper is quite handy tool of Intellij IDEA. The additional source code for the UI design that you do by default it generated into the *.class files. This might not be so useful for the project setup, for example if you use maven as a build tool. So what you need is to tell Intellij that the extra code generated by the JFormDeveloper needs to go into your *.java files.
You can do this by setting this from preference panel: Preferences, search "Gui", GUI Designer