This was a weird one and occurred twice to me. When I start up an app, I would get this error. This didn’t occur with all apps and sometimes not even on previous deployments of the same app.
It was only today that I finally found the cause.
Sometimes when I generate accessors on a Java class and have the “Notify listeners… ” option selected, JDeveloper for some reason adds imports of java.beans.PropertyChangeListener and java.beans.PropertyChangeSupport. This should have been the namesakes from the “oracle.adfmf.java.beans” package.
I don’t what triggers this behaviour. However, I have seen that it happens only on certain JDeveloper workspaces/applications and not all of them.
The fix is simply to change the imports to the right adfmf package.