public <T> void onChanged(SetChangeListener.Change<? super T> change) { if (change.wasAdded()) { out.printf("Added: %s", change.getElementAdded()); } else if (change.wasRemoved()) { out.printf("Removed: %s", change.getElementRemoved()); } out.printf(", Set after the change: %s\n", change.getSet()); }