IntelliJ IDEA - GUI Designer - Cannot preview form

Question

When I create a GUI form in IntelliJ IDEA, clicking on the Preview menu item creates the Error:

Cannot preview form '.../Main.form' Reason: Class not found: javax.swing.JPanel

However, manually creating a main method in the linked class and running the latter, will create my application window without problems:

public static void main(String[] args) {
    JFrame frame = new JFrame("UBPrivacy");
    frame.setContentPane(new Main().panel1);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.pack();
    frame.setVisible(true);
}

In my project structure, I have chosen Project SDK: java 9.0.1
In my platform settings, SDK 9.0 has all the necessary paths configured (java.desktop, etc.).

I wonder if this is an IntelliJ IDEA bug or if I somehow misconfigured my classpath, modules or something else. (Since my manual main RUN works successfully.)

Thanks in advance for any help on this topic.

Answer 1

2 Years late and the bug still persists...

For anyone that re-discovered this question. You need to downgrade your project SDK from Java 9,10,11 to Java 8