I have a real trubble for a beginner)
When I try to see Preview while working in GUIform (even when class is empty), I see an error:
Cannot preview form '.../SimpleG.form'
Reason: cannot load /com/intellij/uiDesigner/FormPreviewFrame.class
// I have installed plugin JFormDesigner and didn't find how/where to install UIDesigner plugin.
Project SDK 1.8;
Project language level SDK default (8)