public interface NewProductContract {
  interface Model {
    interface OnAddProductListener {
      void onAddProductSuccess(Product newProduct);
      void onAddProductError(String message);
    }
    void addProduct(Product product, OnAddProductListener listener);
    . . .
 }

  interface View {
    void addProduct(android.view.View view);
    . . .
  }

  interface Presenter {
    void addProduct(String name, String category, String quantity, String price, boolean important, byte[] productImage);
    . . .
  }
}