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/**
 * Copyright (c) 2016-present, RxJava Contributors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
 * compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License is
 * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
 * the License for the specific language governing permissions and limitations under the License.
 */

package io.reactivex;

import io.reactivex.annotations.*;
import io.reactivex.disposables.Disposable;

/**
 * Provides a mechanism for receiving push-based notification of a single value, an error or completion without any value.
 * 

* When a {@code MaybeObserver} is subscribed to a {@link MaybeSource} through the {@link MaybeSource#subscribe(MaybeObserver)} method, * the {@code MaybeSource} calls {@link #onSubscribe(Disposable)} with a {@link Disposable} that allows * disposing the sequence at any time. A well-behaved * {@code MaybeSource} will call a {@code MaybeObserver}'s {@link #onSuccess(Object)}, {@link #onError(Throwable)} * or {@link #onComplete()} method exactly once as they are considered mutually exclusive terminal signals. *

* Calling the {@code MaybeObserver}'s method must happen in a serialized fashion, that is, they must not * be invoked concurrently by multiple threads in an overlapping fashion and the invocation pattern must * adhere to the following protocol: *

    onSubscribe (onSuccess | onError | onComplete)?
*

* Note that unlike with the {@code Observable} protocol, {@link #onComplete()} is not called after the success item has been * signalled via {@link #onSuccess(Object)}. *

* Subscribing a {@code MaybeObserver} to multiple {@code MaybeSource}s is not recommended. If such reuse * happens, it is the duty of the {@code MaybeObserver} implementation to be ready to receive multiple calls to * its methods and ensure proper concurrent behavior of its business logic. *

* Calling {@link #onSubscribe(Disposable)}, {@link #onSuccess(Object)} or {@link #onError(Throwable)} with a * {@code null} argument is forbidden. *

* The implementations of the {@code onXXX} methods should avoid throwing runtime exceptions other than the following cases: *

    *
  • If the argument is {@code null}, the methods can throw a {@code NullPointerException}. * Note though that RxJava prevents {@code null}s to enter into the flow and thus there is generally no * need to check for nulls in flows assembled from standard sources and intermediate operators. *
  • *
  • If there is a fatal error (such as {@code VirtualMachineError}).
  • *
* @see ReactiveX documentation: Observable * @param * the type of item the MaybeObserver expects to observe * @since 2.0 */ public interface MaybeObserver { /** * Provides the MaybeObserver with the means of cancelling (disposing) the * connection (channel) with the Maybe in both * synchronous (from within {@code onSubscribe(Disposable)} itself) and asynchronous manner. * @param d the Disposable instance whose {@link Disposable#dispose()} can * be called anytime to cancel the connection */ void onSubscribe(@NonNull Disposable d); /** * Notifies the MaybeObserver with one item and that the {@link Maybe} has finished sending * push-based notifications. *

* The {@link Maybe} will not call this method if it calls {@link #onError}. * * @param t * the item emitted by the Maybe */ void onSuccess(@NonNull T t); /** * Notifies the MaybeObserver that the {@link Maybe} has experienced an error condition. *

* If the {@link Maybe} calls this method, it will not thereafter call {@link #onSuccess}. * * @param e * the exception encountered by the Maybe */ void onError(@NonNull Throwable e); /** * Called once the deferred computation completes normally. */ void onComplete(); }





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