public class View {

   @Inject
   void updateFolder(@Named(IServiceConstants.ACTIVE_SELECTION) IFolder folder) {
      // Do something when selection changes
   }
}

public class View extends ViewPart {
   public void createPartControl(Composite parent) {
      getSite().getSelectionProvider().addSelectionChangedListener(new ISelectionChangedListener() {
         public void selectionChanged(SelectionChangedEvent event) {
            if( event.getSelection() instanceof IStructuredSelection) {
               Object o = ((IstructuredSelection)event.getSelection()).getFirstElement();
               if( o instanceof IFolder ) {
                  updateFolder((IFolder) o);
               }
            }
         }
      });
   }
   void updateFolder(IFolder folder) {
      // Do something when selection changes
   }
}

public class ButtonListener {

   @Inject
   public void buttonSelected(@Named(IServiceConstants.ACTIVE_SELECTION) Button button) {
      System.out.println("Somebody pushed a button!");
   }
}