public interface Receiver {

    // Receive individual messages or batches of messages
    default void receive (Message msg) { ... }
    default void receive (MessageBatch batch) { ... }

    // Notification about membership view change
    default void viewAccepted (View new_view) { ... }

    // Notification to temporarily suspend sending messages
    default void block () { ... }
    default void unblock () { ... }

    // Group members can share state
    default void getState (OutputStream output) { ... }
    default void setState (InputStream input) { ... }
}