Annotation Interface MainWindow

@Target(TYPE)
@Retention(RUNTIME)
@Inherited
public @interface MainWindow

Marks a JFrame subclass as the migrated app's main window. The annotated frame renders inline as the content of a MainWindowRoute-extending Vaadin route, peered over SJPanel (Div-backed) instead of the regular SJFrame (Dialog-backed). At most one @MainWindow-annotated class may be instantiated per JVM — detected lazily via the JFrame ctor's CAS check.

Per D_jframe_as_route:

• Inherited — user-code subclasses inherit the annotation from their @MainWindow-annotated parent.
• Target(TYPE) — class-level only.
• Retention(RUNTIME) — visible to the ctor's isAnnotationPresent check.

Typical usage:

@MainWindow
public class MyMainFrame extends JFrame { ... }

public static void mainUI() {
    new MyMainFrame().setVisible(true);
}