chaxiu

val user = getUserInfo()
val friendList = getFriendList(user)
val feedList = getFeedList(friendList)

chaxiu

getUserInfo(new CallBack() {
    @Override
    public void onSuccess(String response) {
        if (response != null) {
            System.out.println(response);
        }
    }
});

chaxiu

getUserInfo(new CallBack() {
    @Override
    public void onSuccess(String user) {
        if (user != null) {
            System.out.println(user);
            getFriendList(user, new CallBack() {
                @Override
                public void onSuccess(String friendList) {
                    if (friendList != null) {
                        System.out.println(friendList);

chaxiu

// delay(1000L) representing request to server

//Suspending Function
// ↓
suspend fun getUserInfo(): String {
    withContext(Dispatchers.IO) {
        delay(1000L)
    }
    return "BoyCoder"
}

chaxiu

suspend fun getUserInfo(): String {
    withContext(Dispatchers.IO) {
        delay(1000L)
    }
    return "BoyCoder"
}

chaxiu

//                          Continuation is nothing but CallBack
//                                         ↓         
public static final Object getUserInfo(Continuation $completion) {
  ...
  return "BoyCoder";
}

chaxiu

public interface Continuation<in T> {
    public val context: CoroutineContext
//   just like: onSuccess(result)
//                 ↓         ↓
    public fun resumeWith(result: Result<T>)
}

chaxiu

interface CallBack {
    void onSuccess(String response);
}

chaxiu

suspend fun getUserInfo(): String {
    withContext(Dispatchers.IO) {
        delay(1000L)
    }
    return "BoyCoder"
}

chaxiu

// suspend modifier
// ↓
suspend fun noSuspendFriendList(user: String): String{
    // body is just like normal function
    return "Tom, Jack"
}