Compare1.java

package test;

import java.util.concurrent.CompletableFuture;
import java.util.function.Consumer;

public class Compare1 {
    // implementations are omitted
    class User {
        String getProfileId() { return null; }
        String getEmail() { return null; }
    }

    class Synchronous {
        <T> T fetchFromDb(Class<T> entityClass, long id) { return null; }
        String sendHttpGet(String url) { return null; }
        void sendEmail(String to, String content) { }

        void runBusinessProcess() {
            User user = fetchFromDb(User.class, 42);
            String profile = sendHttpGet("http://profile_service/get/" + user.getProfileId());
            sendEmail(user.getEmail(), "Your profile is: " + profile);
        }
    }

    class Callbacks {
        <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) { }

        void runBusinessProcess(Runnable callback) {
            fetchFromDb(User.class, 42,
                    user -> sendHttpGet("http://profile_service/get/" + user.getProfileId(),
                            profile -> sendEmail(user.getEmail(), "Your profile is: " + profile,
                                    callback)));
        }
    }

    class Wrappers {
        <T> CompletableFuture<T> fetchFromDb(Class<T> entityClass, long id) { return null; }
        CompletableFuture<String> sendHttpGet(String url) { return null; }
        CompletableFuture<Void> sendEmail(String to, String content) { return null; }

        CompletableFuture<Void> runBusinessProcess() {
            return fetchFromDb(User.class, 42).thenCompose(user -> {
                CompletableFuture<String> httpResult = 
                  sendHttpGet("http://profile_service/get/" + user.getProfileId());
              
                return httpResult.thenCompose(profile ->
                        sendEmail(user.getEmail(), "Your profile is: " + profile));
            });
        }
    }
}