gistfile1.java

public class NewCallbackClient implements SimpleDispatcher.Listener {
    public void onItemSetChanged(SimpleDispatcher dispatcher) {
        System.out.println("onItemSetChanged");
    }

    public void onItemDataChanged(SimpleDispatcher dispatcher, int itemId, int changeMask) {
        if ((changeMask & Item.FIELD_1) != 0) {
            System.out.println("onItemDataChanged: " + dispatcher.getItemById(itemId));
        }
    }
}

class SimpleDispatcher {
    private SparseArray<Item> array = new SparseArray<Item>();

    public Item getItemById(int id) {
        return array.get(id);
    }

    public Collection<Item> enumItems() {
        ...
    }

    public interface Listener {
        void onItemSetChanged(SimpleDispatcher dispatcher);
        void onItemDataChanged(SimpleDispatcher dispatcher, int itemId, int changeMask);
    }
}

class Item {
    public static final int FIELD_1 = 1, FIELD_2 = 2, FIELD_3 = 4;

    int field1, field2;
    String field3;
}