You can set the size and the position of the widget via xml or programmatically. The default layout for swing that is used is the XYLayout. This is mostly used for eg business applications that have to run on a specific client (only tested under win32 btw). In ApplicationPart in the method activate() the widget is added to a swing JPanel and this will call the XYLayout manager. So size and position are only set on initial activation and are never refreshed. Setting sizes will not come to a refresh of the widget, but when setting the gui calls the layoutmanager again, it will layout it according to the size being set.