Plugins register EBComponent instances with the EditBus to receive messages reflecting changes in jEdit's state.

The message classes derived from EBMessage cover the opening and closing of the application, changes in the status of buffers and views, changes in user settings, as well as changes in the state of other program features. A full list of messages can be found in the org.gjt.sp.jedit.msg package.

EBComponents are added and removed with the EditBus.addToBus() and EditBus.removeFromBus() methods.

Typically, the EBComponent.handleMessage() method is implemented with one or more if blocks that test whether the message is an instance of a derived message class in which the component has an interest.

if(msg instanceof BufferUpdate) {
    // a buffer's state has changed!
}
else if(msg instanceof ViewUpdate) {
    // a view's state has changed!
}
// ... and so on

If a plugin core class will respond to EditBus messages, it can be derived from EBPlugin, in which case no explicit addToBus() call is necessary. Otherwise, EditPlugin will suffice as a plugin base class. Note that QuickNotepad uses the latter.