Just wondering what the opposing framework in Java would be for creating modular GUI applications, with things like event aggregation, etc.
I know for Java there isn't a single definitive GUI framework, and so far I've seen the Eclipse RCP and Netbeans Platform, however these don't seem to do these kind of things.
I'm a .Net developer looking to transition across to Java, and please excuse my ignorance if the question doesn't make complete sense.
You are looking for application frameworks or rich client platforms, so Eclipse RCP if the right direction.
Eclipse builds on OSGI and that means that any module (called Eclipse Plug-In or OSGi Bundle) can either register its own services or makeuse of any other service provided by any other module. The Eclipse RCP platform comes with a lot of handy services, esp. in the meaning of Workbench-level services like ISelectionService where you can hook in to retrieve selection events. These selection events are already on a higher abstraction level, they don't contain mouse x/y coordinates but merely the Object(s) being selected such as a "Java Source File" in the Eclipse JDT case. There are menu manager services , selection services, event handling services, administration services, preferences services, action and command handler services etc.
If i understand event aggregation correctly, it manages a list of events and subscribers, and manages the forwarding of these events to whoever has subscribed to a given event. This seems basically what Eclipse already covers under the hood, e.g. with the OSGi EventAdmin, but this is very low level.