public class MyEditor extends TextEditor {
         ....
         @Override
	public boolean isDirty() {		
		return mIsDirty;
	}
        
        @Override public void createPartControl(Composite pParent) {
        .....
        mDocumentUndoManager = DocumentUndoManagerRegistry.getDocumentUndoManager(getSourceViewer().getDocument());
		OperationHistoryFactory.getOperationHistory().addOperationHistoryListener(e -> {
			if (e.getOperation().hasContext(mDocumentUndoManager.getUndoContext())) {
				// if there is no more operation to undo
				if (!OperationHistoryFactory.getOperationHistory().canUndo(mDocumentUndoManager.getUndoContext())) {
					mIsDirty = false;
				} else {
					mIsDirty = true;
				}
				firePropertyChange(IEditorPart.PROP_DIRTY);
			}
		});
        }

}