Compare1c.java

class Callbacks {
    // I/O operations: non-blocking, asynchronous
    <T> void fetchFromDb(Class<T> entityClass, long id, Consumer<T> callback) { }
    void sendHttpGet(String url, Consumer<String> callback) { }
    void sendEmail(String to, String content, Runnable callback) { }

    // the bussines logic: asynchronous
    void runBusinessProcess(Runnable callback) {
        fetchFromDb(User.class, 42,
                // continuation: what should happen after the user is read from the db    
                user -> sendHttpGet("http://profile_service/get/" + user.getProfileId(),
                        profile -> sendEmail(user.getEmail(), 
                                "Your profile is: " + profile,
                                callback)));
    }
}