George,
Matisse forms aren’t portable between different toolsets. To modify Matisse forms, you need the Matisse tool. If such a plug-in is not available in JDeveloper, then you can’t modify the form as a Matisse form. However, the generated Java code doesn’t require Matisse to work and may be usable with other IDEs that have a GUI builder. Matisse forms consist of a file (extension .form) that describes the gui elements in a way the Matisse can understand, plus a Java file that consists largely of code generated by the Matisse tool. Unfortunately, we don’t have any expertise with JDeveloper to help you migrate from one IDE to the other. If JDeveloper has a GUI development tool, it may work with the Java file, but not with the .form file, unless it has an implementation of Matisse.
Note that Matisse will likely not be enhanced in future releases of MyEclipse (though bugs will be addressed), so we’d encourage you to move to WindowBuilder, with its Swing Developer, which is available as a free eclipse plug-in from the Eclipse organisation (and can be installed on MyEclipse, via its Configuration Center). Window Builder does not rely on a secondary description file so that may be a better option for you, if you are not heavily invested in Matisse.