Use API described bellow to show Notifications (a balloon windows on the bottom right corner of application window) and appending text into a Message Window.
NotificationManager
This is an entry point to display notifications in MagicDraw. Two types of notifications can be displayed: application level and container level. Container lever notifications are displayed in special container that implements com.nomagic.ui.notification.NotificationsContainer interface.
Use com.nomagic.magicdraw.ui.notification.NotificationManage.
Use com.nomagic.magicdraw.core.GUILog.log(java.lang.String) to add some information into a Message Window,
com.nomagic.magicdraw.ui.notification.Notification.getContext() controls where notification is logged in the Message Window - into Environment or Project tab.
GUILog
Use GUILog.log(java.lang.String) to put a text into Project Message Window message.
Use GUILog.log(Notification, boolean) to log information from notification into a Message Window.
Use GUILog.openLog() to open Message Window.
For more details about every specific kind of a property, see javadoc.
You can find the code examples in <installation_directory>/openapi/examples/notifications