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Maybe.java
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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 java.util.NoSuchElementException;
import java.util.concurrent.*;
import org.reactivestreams.*;
import io.reactivex.annotations.*;
import io.reactivex.disposables.Disposable;
import io.reactivex.exceptions.Exceptions;
import io.reactivex.functions.*;
import io.reactivex.internal.functions.*;
import io.reactivex.internal.fuseable.*;
import io.reactivex.internal.observers.BlockingMultiObserver;
import io.reactivex.internal.operators.flowable.*;
import io.reactivex.internal.operators.maybe.*;
import io.reactivex.internal.operators.mixed.*;
import io.reactivex.internal.util.*;
import io.reactivex.observers.TestObserver;
import io.reactivex.plugins.RxJavaPlugins;
import io.reactivex.schedulers.Schedulers;
/**
* The {@code Maybe} class represents a deferred computation and emission of a single value, no value at all or an exception.
* <p>
* The {@code Maybe} class implements the {@link MaybeSource} base interface and the default consumer
* type it interacts with is the {@link MaybeObserver} via the {@link #subscribe(MaybeObserver)} method.
* <p>
* The {@code Maybe} operates with the following sequential protocol:
* <pre><code>
* onSubscribe (onSuccess | onError | onComplete)?
* </code></pre>
* <p>
* Note that {@code onSuccess}, {@code onError} and {@code onComplete} are mutually exclusive events; unlike {@code Observable},
* {@code onSuccess} is never followed by {@code onError} or {@code onComplete}.
* <p>
* Like {@link Observable}, a running {@code Maybe} can be stopped through the {@link Disposable} instance
* provided to consumers through {@link MaybeObserver#onSubscribe}.
* <p>
* Like an {@code Observable}, a {@code Maybe} is lazy, can be either "hot" or "cold", synchronous or
* asynchronous. {@code Maybe} instances returned by the methods of this class are <em>cold</em>
* and there is a standard <em>hot</em> implementation in the form of a subject:
* {@link io.reactivex.subjects.MaybeSubject MaybeSubject}.
* <p>
* The documentation for this class makes use of marble diagrams. The following legend explains these diagrams:
* <p>
* <img width="640" height="370" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/maybe.png" alt="">
* <p>
* See {@link Flowable} or {@link Observable} for the
* implementation of the Reactive Pattern for a stream or vector of values.
* <p>
* Example:
* <pre><code>
* Disposable d = Maybe.just("Hello World")
* .delay(10, TimeUnit.SECONDS, Schedulers.io())
* .subscribeWith(new DisposableMaybeObserver<String>() {
* @Override
* public void onStart() {
* System.out.println("Started");
* }
*
* @Override
* public void onSuccess(String value) {
* System.out.println("Success: " + value);
* }
*
* @Override
* public void onError(Throwable error) {
* error.printStackTrace();
* }
*
* @Override
* public void onComplete() {
* System.out.println("Done!");
* }
* });
*
* Thread.sleep(5000);
*
* d.dispose();
* </code></pre>
* <p>
* Note that by design, subscriptions via {@link #subscribe(MaybeObserver)} can't be disposed
* from the outside (hence the
* {@code void} return of the {@link #subscribe(MaybeObserver)} method) and it is the
* responsibility of the implementor of the {@code MaybeObserver} to allow this to happen.
* RxJava supports such usage with the standard
* {@link io.reactivex.observers.DisposableMaybeObserver DisposableMaybeObserver} instance.
* For convenience, the {@link #subscribeWith(MaybeObserver)} method is provided as well to
* allow working with a {@code MaybeObserver} (or subclass) instance to be applied with in
* a fluent manner (such as in the example above).
*
* @param <T> the value type
* @since 2.0
* @see io.reactivex.observers.DisposableMaybeObserver
*/
public abstract class Maybe<T> implements MaybeSource<T> {
/**
* Runs multiple MaybeSources and signals the events of the first one that signals (disposing
* the rest).
* <p>
* <img width="640" height="519" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Maybe.amb.png" alt="">
* <dl>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code amb} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
* @param <T> the value type
* @param sources the Iterable sequence of sources. A subscription to each source will
* occur in the same order as in the Iterable.
* @return the new Maybe instance
*/
@CheckReturnValue
@NonNull
@SchedulerSupport(SchedulerSupport.NONE)
public static <T> Maybe<T> amb(final Iterable<? extends MaybeSource<? extends T>> sources) {
ObjectHelper.requireNonNull(sources, "sources is null");
return RxJavaPlugins.onAssembly(new MaybeAmb<T>(null, sources));
}
/**
* Runs multiple MaybeSources and signals the events of the first one that signals (disposing
* the rest).
* <p>
* <img width="640" height="519" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Maybe.ambArray.png" alt="">
* <dl>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code ambArray} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
* @param <T> the value type
* @param sources the array of sources. A subscription to each source will
* occur in the same order as in the array.
* @return the new Maybe instance
*/
@CheckReturnValue
@SchedulerSupport(SchedulerSupport.NONE)
@SuppressWarnings("unchecked")
public static <T> Maybe<T> ambArray(final MaybeSource<? extends T>... sources) {
if (sources.length == 0) {
return empty();
}
if (sources.length == 1) {
return wrap((MaybeSource<T>)sources[0]);
}
return RxJavaPlugins.onAssembly(new MaybeAmb<T>(sources, null));
}
/**
* Concatenate the single values, in a non-overlapping fashion, of the MaybeSource sources provided by
* an Iterable sequence.
* <p>
* <img width="640" height="526" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Maybe.concat.i.png" alt="">
* <dl>
* <dt><b>Backpressure:</b></dt>
* <dd>The returned {@code Flowable} honors the backpressure of the downstream consumer.</dd>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code concat} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
* @param <T> the value type
* @param sources the Iterable sequence of MaybeSource instances
* @return the new Flowable instance
*/
@BackpressureSupport(BackpressureKind.FULL)
@CheckReturnValue
@NonNull
@SchedulerSupport(SchedulerSupport.NONE)
public static <T> Flowable<T> concat(Iterable<? extends MaybeSource<? extends T>> sources) {
ObjectHelper.requireNonNull(sources, "sources is null");
return RxJavaPlugins.onAssembly(new MaybeConcatIterable<T>(sources));
}
/**
* Returns a Flowable that emits the items emitted by two MaybeSources, one after the other.
* <p>
* <img width="640" height="422" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Maybe.concat.png" alt="">
* <dl>
* <dt><b>Backpressure:</b></dt>
* <dd>The returned {@code Flowable} honors the backpressure of the downstream consumer.</dd>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code concat} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
*
* @param <T> the common value type
* @param source1
* a MaybeSource to be concatenated
* @param source2
* a MaybeSource to be concatenated
* @return a Flowable that emits items emitted by the two source MaybeSources, one after the other.
* @see <a href="http://reactivex.io/documentation/operators/concat.html">ReactiveX operators documentation: Concat</a>
*/
@BackpressureSupport(BackpressureKind.FULL)
@CheckReturnValue
@NonNull
@SchedulerSupport(SchedulerSupport.NONE)
@SuppressWarnings("unchecked")
public static <T> Flowable<T> concat(MaybeSource<? extends T> source1, MaybeSource<? extends T> source2) {
ObjectHelper.requireNonNull(source1, "source1 is null");
ObjectHelper.requireNonNull(source2, "source2 is null");
return concatArray(source1, source2);
}
/**
* Returns a Flowable that emits the items emitted by three MaybeSources, one after the other.
* <p>
* <img width="640" height="422" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Maybe.concat.png" alt="">
* <dl>
* <dt><b>Backpressure:</b></dt>
* <dd>The returned {@code Flowable} honors the backpressure of the downstream consumer.</dd>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code concat} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
*
* @param <T> the common value type
* @param source1
* a MaybeSource to be concatenated
* @param source2
* a MaybeSource to be concatenated
* @param source3
* a MaybeSource to be concatenated
* @return a Flowable that emits items emitted by the three source MaybeSources, one after the other.
* @see <a href="http://reactivex.io/documentation/operators/concat.html">ReactiveX operators documentation: Concat</a>
*/
@BackpressureSupport(BackpressureKind.FULL)
@CheckReturnValue
@NonNull
@SchedulerSupport(SchedulerSupport.NONE)
@SuppressWarnings("unchecked")
public static <T> Flowable<T> concat(
MaybeSource<? extends T> source1, MaybeSource<? extends T> source2, MaybeSource<? extends T> source3) {
ObjectHelper.requireNonNull(source1, "source1 is null");
ObjectHelper.requireNonNull(source2, "source2 is null");
ObjectHelper.requireNonNull(source3, "source3 is null");
return concatArray(source1, source2, source3);
}
/**
* Returns a Flowable that emits the items emitted by four MaybeSources, one after the other.
* <p>
* <img width="640" height="422" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Maybe.concat.png" alt="">
* <dl>
* <dt><b>Backpressure:</b></dt>
* <dd>The returned {@code Flowable} honors the backpressure of the downstream consumer.</dd>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code concat} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
*
* @param <T> the common value type
* @param source1
* a MaybeSource to be concatenated
* @param source2
* a MaybeSource to be concatenated
* @param source3
* a MaybeSource to be concatenated
* @param source4
* a MaybeSource to be concatenated
* @return a Flowable that emits items emitted by the four source MaybeSources, one after the other.
* @see <a href="http://reactivex.io/documentation/operators/concat.html">ReactiveX operators documentation: Concat</a>
*/
@BackpressureSupport(BackpressureKind.FULL)
@CheckReturnValue
@NonNull
@SchedulerSupport(SchedulerSupport.NONE)
@SuppressWarnings("unchecked")
public static <T> Flowable<T> concat(
MaybeSource<? extends T> source1, MaybeSource<? extends T> source2, MaybeSource<? extends T> source3, MaybeSource<? extends T> source4) {
ObjectHelper.requireNonNull(source1, "source1 is null");
ObjectHelper.requireNonNull(source2, "source2 is null");
ObjectHelper.requireNonNull(source3, "source3 is null");
ObjectHelper.requireNonNull(source4, "source4 is null");
return concatArray(source1, source2, source3, source4);
}
/**
* Concatenate the single values, in a non-overlapping fashion, of the MaybeSource sources provided by
* a Publisher sequence.
* <p>
* <img width="640" height="416" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Maybe.concat.p.png" alt="">
* <dl>
* <dt><b>Backpressure:</b></dt>
* <dd>The returned {@code Flowable} honors the backpressure of the downstream consumer and
* expects the {@code Publisher} to honor backpressure as well. If the sources {@code Publisher}
* violates this, a {@link io.reactivex.exceptions.MissingBackpressureException} is signalled.</dd>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code concat} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
* @param <T> the value type
* @param sources the Publisher of MaybeSource instances
* @return the new Flowable instance
*/
@BackpressureSupport(BackpressureKind.FULL)
@CheckReturnValue
@SchedulerSupport(SchedulerSupport.NONE)
public static <T> Flowable<T> concat(Publisher<? extends MaybeSource<? extends T>> sources) {
return concat(sources, 2);
}
/**
* Concatenate the single values, in a non-overlapping fashion, of the MaybeSource sources provided by
* a Publisher sequence.
* <p>
* <img width="640" height="416" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Maybe.concat.pn.png" alt="">
* <dl>
* <dt><b>Backpressure:</b></dt>
* <dd>The returned {@code Flowable} honors the backpressure of the downstream consumer and
* expects the {@code Publisher} to honor backpressure as well. If the sources {@code Publisher}
* violates this, a {@link io.reactivex.exceptions.MissingBackpressureException} is signalled.</dd>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code concat} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
* @param <T> the value type
* @param sources the Publisher of MaybeSource instances
* @param prefetch the number of MaybeSources to prefetch from the Publisher
* @return the new Flowable instance
*/
@BackpressureSupport(BackpressureKind.FULL)
@CheckReturnValue
@NonNull
@SchedulerSupport(SchedulerSupport.NONE)
@SuppressWarnings({ "unchecked", "rawtypes" })
public static <T> Flowable<T> concat(Publisher<? extends MaybeSource<? extends T>> sources, int prefetch) {
ObjectHelper.requireNonNull(sources, "sources is null");
ObjectHelper.verifyPositive(prefetch, "prefetch");
return RxJavaPlugins.onAssembly(new FlowableConcatMapPublisher(sources, MaybeToPublisher.instance(), prefetch, ErrorMode.IMMEDIATE));
}
/**
* Concatenate the single values, in a non-overlapping fashion, of the MaybeSource sources in the array.
* <p>
* <img width="640" height="526" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Maybe.concatArray.png" alt="">
* <dl>
* <dt><b>Backpressure:</b></dt>
* <dd>The returned {@code Flowable} honors the backpressure of the downstream consumer.</dd>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code concatArray} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
* @param <T> the value type
* @param sources the array of MaybeSource instances
* @return the new Flowable instance
*/
@BackpressureSupport(BackpressureKind.FULL)
@CheckReturnValue
@NonNull
@SchedulerSupport(SchedulerSupport.NONE)
@SuppressWarnings("unchecked")
public static <T> Flowable<T> concatArray(MaybeSource<? extends T>... sources) {
ObjectHelper.requireNonNull(sources, "sources is null");
if (sources.length == 0) {
return Flowable.empty();
}
if (sources.length == 1) {
return RxJavaPlugins.onAssembly(new MaybeToFlowable<T>((MaybeSource<T>)sources[0]));
}
return RxJavaPlugins.onAssembly(new MaybeConcatArray<T>(sources));
}
/**
* Concatenates a variable number of MaybeSource sources and delays errors from any of them
* till all terminate.
* <p>
* <img width="640" height="425" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Maybe.concatArrayDelayError.png" alt="">
* <dl>
* <dt><b>Backpressure:</b></dt>
* <dd>The operator honors backpressure from downstream.</dd>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code concatArrayDelayError} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
* @param sources the array of sources
* @param <T> the common base value type
* @return the new Flowable instance
* @throws NullPointerException if sources is null
*/
@SuppressWarnings("unchecked")
@BackpressureSupport(BackpressureKind.FULL)
@CheckReturnValue
@SchedulerSupport(SchedulerSupport.NONE)
public static <T> Flowable<T> concatArrayDelayError(MaybeSource<? extends T>... sources) {
if (sources.length == 0) {
return Flowable.empty();
} else
if (sources.length == 1) {
return RxJavaPlugins.onAssembly(new MaybeToFlowable<T>((MaybeSource<T>)sources[0]));
}
return RxJavaPlugins.onAssembly(new MaybeConcatArrayDelayError<T>(sources));
}
/**
* Concatenates a sequence of MaybeSource eagerly into a single stream of values.
* <p>
* Eager concatenation means that once a subscriber subscribes, this operator subscribes to all of the
* source MaybeSources. The operator buffers the value emitted by these MaybeSources and then drains them
* in order, each one after the previous one completes.
* <p>
* <img width="640" height="489" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Maybe.concatArrayEager.png" alt="">
* <dl>
* <dt><b>Backpressure:</b></dt>
* <dd>The operator honors backpressure from downstream.</dd>
* <dt><b>Scheduler:</b></dt>
* <dd>This method does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
* @param <T> the value type
* @param sources a sequence of MaybeSources that need to be eagerly concatenated
* @return the new Flowable instance with the specified concatenation behavior
*/
@SuppressWarnings({ "rawtypes", "unchecked" })
@BackpressureSupport(BackpressureKind.FULL)
@CheckReturnValue
@SchedulerSupport(SchedulerSupport.NONE)
public static <T> Flowable<T> concatArrayEager(MaybeSource<? extends T>... sources) {
return Flowable.fromArray(sources).concatMapEager((Function)MaybeToPublisher.instance());
}
/**
* Concatenates the Iterable sequence of MaybeSources into a single sequence by subscribing to each MaybeSource,
* one after the other, one at a time and delays any errors till the all inner MaybeSources terminate.
* <p>
* <img width="640" height="469" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Maybe.concatDelayError.i.png" alt="">
* <dl>
* <dt><b>Backpressure:</b></dt>
* <dd>The operator honors backpressure from downstream.</dd>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code concatDelayError} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
*
* @param <T> the common element base type
* @param sources the Iterable sequence of MaybeSources
* @return the new Flowable with the concatenating behavior
*/
@SuppressWarnings({ "unchecked", "rawtypes" })
@BackpressureSupport(BackpressureKind.FULL)
@CheckReturnValue
@NonNull
@SchedulerSupport(SchedulerSupport.NONE)
public static <T> Flowable<T> concatDelayError(Iterable<? extends MaybeSource<? extends T>> sources) {
ObjectHelper.requireNonNull(sources, "sources is null");
return Flowable.fromIterable(sources).concatMapDelayError((Function)MaybeToPublisher.instance());
}
/**
* Concatenates the Publisher sequence of Publishers into a single sequence by subscribing to each inner Publisher,
* one after the other, one at a time and delays any errors till the all inner and the outer Publishers terminate.
* <p>
* <img width="640" height="360" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Maybe.concatDelayError.p.png" alt="">
* <dl>
* <dt><b>Backpressure:</b></dt>
* <dd>{@code concatDelayError} fully supports backpressure.</dd>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code concatDelayError} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
*
* @param <T> the common element base type
* @param sources the Publisher sequence of Publishers
* @return the new Publisher with the concatenating behavior
*/
@SuppressWarnings({ "unchecked", "rawtypes" })
@BackpressureSupport(BackpressureKind.FULL)
@CheckReturnValue
@SchedulerSupport(SchedulerSupport.NONE)
public static <T> Flowable<T> concatDelayError(Publisher<? extends MaybeSource<? extends T>> sources) {
return Flowable.fromPublisher(sources).concatMapDelayError((Function)MaybeToPublisher.instance());
}
/**
* Concatenates a sequence of MaybeSources eagerly into a single stream of values.
* <p>
* Eager concatenation means that once a subscriber subscribes, this operator subscribes to all of the
* source MaybeSources. The operator buffers the values emitted by these MaybeSources and then drains them
* in order, each one after the previous one completes.
* <p>
* <img width="640" height="526" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Maybe.concatEager.i.png" alt="">
* <dl>
* <dt><b>Backpressure:</b></dt>
* <dd>Backpressure is honored towards the downstream.</dd>
* <dt><b>Scheduler:</b></dt>
* <dd>This method does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
* @param <T> the value type
* @param sources a sequence of MaybeSource that need to be eagerly concatenated
* @return the new Flowable instance with the specified concatenation behavior
*/
@SuppressWarnings({ "rawtypes", "unchecked" })
@BackpressureSupport(BackpressureKind.FULL)
@CheckReturnValue
@SchedulerSupport(SchedulerSupport.NONE)
public static <T> Flowable<T> concatEager(Iterable<? extends MaybeSource<? extends T>> sources) {
return Flowable.fromIterable(sources).concatMapEager((Function)MaybeToPublisher.instance());
}
/**
* Concatenates a Publisher sequence of MaybeSources eagerly into a single stream of values.
* <p>
* Eager concatenation means that once a subscriber subscribes, this operator subscribes to all of the
* emitted source Publishers as they are observed. The operator buffers the values emitted by these
* Publishers and then drains them in order, each one after the previous one completes.
* <p>
* <img width="640" height="511" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Maybe.concatEager.p.png" alt="">
* <dl>
* <dt><b>Backpressure:</b></dt>
* <dd>Backpressure is honored towards the downstream and the outer Publisher is
* expected to support backpressure. Violating this assumption, the operator will
* signal {@link io.reactivex.exceptions.MissingBackpressureException}.</dd>
* <dt><b>Scheduler:</b></dt>
* <dd>This method does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
* @param <T> the value type
* @param sources a sequence of Publishers that need to be eagerly concatenated
* @return the new Publisher instance with the specified concatenation behavior
*/
@SuppressWarnings({ "rawtypes", "unchecked" })
@BackpressureSupport(BackpressureKind.FULL)
@CheckReturnValue
@SchedulerSupport(SchedulerSupport.NONE)
public static <T> Flowable<T> concatEager(Publisher<? extends MaybeSource<? extends T>> sources) {
return Flowable.fromPublisher(sources).concatMapEager((Function)MaybeToPublisher.instance());
}
/**
* Provides an API (via a cold Maybe) that bridges the reactive world with the callback-style world.
* <p>
* Example:
* <pre><code>
* Maybe.<Event>create(emitter -> {
* Callback listener = new Callback() {
* @Override
* public void onEvent(Event e) {
* if (e.isNothing()) {
* emitter.onComplete();
* } else {
* emitter.onSuccess(e);
* }
* }
*
* @Override
* public void onFailure(Exception e) {
* emitter.onError(e);
* }
* };
*
* AutoCloseable c = api.someMethod(listener);
*
* emitter.setCancellable(c::close);
*
* });
* </code></pre>
* <dl>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code create} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
* @param <T> the value type
* @param onSubscribe the emitter that is called when a MaybeObserver subscribes to the returned {@code Maybe}
* @return the new Maybe instance
* @see MaybeOnSubscribe
* @see Cancellable
*/
@CheckReturnValue
@NonNull
@SchedulerSupport(SchedulerSupport.NONE)
public static <T> Maybe<T> create(MaybeOnSubscribe<T> onSubscribe) {
ObjectHelper.requireNonNull(onSubscribe, "onSubscribe is null");
return RxJavaPlugins.onAssembly(new MaybeCreate<T>(onSubscribe));
}
/**
* Calls a Supplier for each individual MaybeObserver to return the actual MaybeSource source to
* be subscribed to.
* <dl>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code defer} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
* @param <T> the value type
* @param maybeSupplier the Supplier that is called for each individual MaybeObserver and
* returns a MaybeSource instance to subscribe to
* @return the new Maybe instance
*/
@CheckReturnValue
@NonNull
@SchedulerSupport(SchedulerSupport.NONE)
public static <T> Maybe<T> defer(final Supplier<? extends MaybeSource<? extends T>> maybeSupplier) {
ObjectHelper.requireNonNull(maybeSupplier, "maybeSupplier is null");
return RxJavaPlugins.onAssembly(new MaybeDefer<T>(maybeSupplier));
}
/**
* Returns a (singleton) Maybe instance that calls {@link MaybeObserver#onComplete onComplete}
* immediately.
* <p>
* <img width="640" height="190" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/empty.png" alt="">
* <dl>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code empty} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
* @param <T> the value type
* @return the new Maybe instance
*/
@CheckReturnValue
@SchedulerSupport(SchedulerSupport.NONE)
@SuppressWarnings("unchecked")
public static <T> Maybe<T> empty() {
return RxJavaPlugins.onAssembly((Maybe<T>)MaybeEmpty.INSTANCE);
}
/**
* Returns a Maybe that invokes a subscriber's {@link MaybeObserver#onError onError} method when the
* subscriber subscribes to it.
* <p>
* <img width="640" height="447" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Maybe.error.png" alt="">
* <dl>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code error} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
*
* @param exception
* the particular Throwable to pass to {@link MaybeObserver#onError onError}
* @param <T>
* the type of the item (ostensibly) emitted by the Maybe
* @return a Maybe that invokes the subscriber's {@link MaybeObserver#onError onError} method when
* the subscriber subscribes to it
* @see <a href="http://reactivex.io/documentation/operators/empty-never-throw.html">ReactiveX operators documentation: Throw</a>
*/
@CheckReturnValue
@NonNull
@SchedulerSupport(SchedulerSupport.NONE)
public static <T> Maybe<T> error(Throwable exception) {
ObjectHelper.requireNonNull(exception, "exception is null");
return RxJavaPlugins.onAssembly(new MaybeError<T>(exception));
}
/**
* Returns a Maybe that invokes a {@link MaybeObserver}'s {@link MaybeObserver#onError onError} method when the
* MaybeObserver subscribes to it.
* <p>
* <img width="640" height="190" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/error.png" alt="">
* <dl>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code error} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
*
* @param supplier
* a Supplier factory to return a Throwable for each individual MaybeObserver
* @param <T>
* the type of the items (ostensibly) emitted by the Maybe
* @return a Maybe that invokes the {@link MaybeObserver}'s {@link MaybeObserver#onError onError} method when
* the MaybeObserver subscribes to it
* @see <a href="http://reactivex.io/documentation/operators/empty-never-throw.html">ReactiveX operators documentation: Throw</a>
*/
@CheckReturnValue
@NonNull
@SchedulerSupport(SchedulerSupport.NONE)
public static <T> Maybe<T> error(Supplier<? extends Throwable> supplier) {
ObjectHelper.requireNonNull(supplier, "errorSupplier is null");
return RxJavaPlugins.onAssembly(new MaybeErrorCallable<T>(supplier));
}
/**
* Returns a Maybe instance that runs the given Action for each subscriber and
* emits either its exception or simply completes.
* <dl>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code fromAction} does not operate by default on a particular {@link Scheduler}.</dd>
* <dt><b>Error handling:</b></dt>
* <dd> If the {@link Action} throws an exception, the respective {@link Throwable} is
* delivered to the downstream via {@link MaybeObserver#onError(Throwable)},
* except when the downstream has disposed this {@code Maybe} source.
* In this latter case, the {@code Throwable} is delivered to the global error handler via
* {@link RxJavaPlugins#onError(Throwable)} as an {@link io.reactivex.exceptions.UndeliverableException UndeliverableException}.
* </dd>
* </dl>
* @param <T> the target type
* @param run the runnable to run for each subscriber
* @return the new Maybe instance
* @throws NullPointerException if run is null
*/
@CheckReturnValue
@NonNull
@SchedulerSupport(SchedulerSupport.NONE)
public static <T> Maybe<T> fromAction(final Action run) {
ObjectHelper.requireNonNull(run, "run is null");
return RxJavaPlugins.onAssembly(new MaybeFromAction<T>(run));
}
/**
* Wraps a CompletableSource into a Maybe.
*
* <dl>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code fromCompletable} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
* @param <T> the target type
* @param completableSource the CompletableSource to convert from
* @return the new Maybe instance
* @throws NullPointerException if completable is null
*/
@CheckReturnValue
@NonNull
@SchedulerSupport(SchedulerSupport.NONE)
public static <T> Maybe<T> fromCompletable(CompletableSource completableSource) {
ObjectHelper.requireNonNull(completableSource, "completableSource is null");
return RxJavaPlugins.onAssembly(new MaybeFromCompletable<T>(completableSource));
}
/**
* Wraps a SingleSource into a Maybe.
*
* <dl>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code fromSingle} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
* @param <T> the target type
* @param singleSource the SingleSource to convert from
* @return the new Maybe instance
* @throws NullPointerException if single is null
*/
@CheckReturnValue
@NonNull
@SchedulerSupport(SchedulerSupport.NONE)
public static <T> Maybe<T> fromSingle(SingleSource<T> singleSource) {
ObjectHelper.requireNonNull(singleSource, "singleSource is null");
return RxJavaPlugins.onAssembly(new MaybeFromSingle<T>(singleSource));
}
/**
* Returns a {@link Maybe} that invokes the given {@link Callable} for each individual {@link MaybeObserver} that
* subscribes and emits the resulting non-null item via {@code onSuccess} while
* considering a {@code null} result from the {@code Callable} as indication for valueless completion
* via {@code onComplete}.
* <p>
* This operator allows you to defer the execution of the given {@code Callable} until a {@code MaybeObserver}
* subscribes to the returned {@link Maybe}. In other terms, this source operator evaluates the given
* {@code Callable} "lazily".
* <p>
* Note that the {@code null} handling of this operator differs from the similar source operators in the other
* {@link io.reactivex base reactive classes}. Those operators signal a {@code NullPointerException} if the value returned by their
* {@code Callable} is {@code null} while this {@code fromCallable} considers it to indicate the
* returned {@code Maybe} is empty.
* <dl>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code fromCallable} does not operate by default on a particular {@link Scheduler}.</dd>
* <dt><b>Error handling:</b></dt>
* <dd>Any non-fatal exception thrown by {@link Callable#call()} will be forwarded to {@code onError},
* except if the {@code MaybeObserver} disposed the subscription in the meantime. In this latter case,
* the exception is forwarded to the global error handler via
* {@link io.reactivex.plugins.RxJavaPlugins#onError(Throwable)} wrapped into a
* {@link io.reactivex.exceptions.UndeliverableException UndeliverableException}.
* Fatal exceptions are rethrown and usually will end up in the executing thread's
* {@link java.lang.Thread.UncaughtExceptionHandler#uncaughtException(Thread, Throwable)} handler.</dd>
* </dl>
*
* @param callable
* a {@link Callable} instance whose execution should be deferred and performed for each individual
* {@code MaybeObserver} that subscribes to the returned {@link Maybe}.
* @param <T>
* the type of the item emitted by the {@link Maybe}.
* @return a new Maybe instance
* @see #defer(Supplier)
* @see #fromSupplier(Supplier)
*/
@CheckReturnValue
@NonNull
@SchedulerSupport(SchedulerSupport.NONE)
public static <T> Maybe<T> fromCallable(@NonNull final Callable<? extends T> callable) {
ObjectHelper.requireNonNull(callable, "callable is null");
return RxJavaPlugins.onAssembly(new MaybeFromCallable<T>(callable));
}
/**
* Converts a {@link Future} into a Maybe, treating a null result as an indication of emptiness.
* <p>
* <img width="640" height="315" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/from.Future.png" alt="">
* <p>
* You can convert any object that supports the {@link Future} interface into a Maybe that emits the
* return value of the {@link Future#get} method of that object, by passing the object into the {@code from}
* method.
* <p>
* <em>Important note:</em> This Maybe is blocking; you cannot dispose it.
* <p>
* Unlike 1.x, disposing the Maybe won't cancel the future. If necessary, one can use composition to achieve the
* cancellation effect: {@code futureMaybe.doOnDispose(() -> future.cancel(true));}.
* <dl>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code fromFuture} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
*
* @param future
* the source {@link Future}
* @param <T>
* the type of object that the {@link Future} returns, and also the type of item to be emitted by
* the resulting Maybe
* @return a Maybe that emits the item from the source {@link Future}
* @see <a href="http://reactivex.io/documentation/operators/from.html">ReactiveX operators documentation: From</a>
*/
@CheckReturnValue
@NonNull
@SchedulerSupport(SchedulerSupport.NONE)
public static <T> Maybe<T> fromFuture(Future<? extends T> future) {
ObjectHelper.requireNonNull(future, "future is null");
return RxJavaPlugins.onAssembly(new MaybeFromFuture<T>(future, 0L, null));
}
/**
* Converts a {@link Future} into a Maybe, with a timeout on the Future.
* <p>
* <img width="640" height="315" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/from.Future.png" alt="">
* <p>
* You can convert any object that supports the {@link Future} interface into a Maybe that emits the
* return value of the {@link Future#get} method of that object, by passing the object into the {@code fromFuture}
* method.
* <p>
* Unlike 1.x, disposing the Maybe won't cancel the future. If necessary, one can use composition to achieve the
* cancellation effect: {@code futureMaybe.doOnCancel(() -> future.cancel(true));}.
* <p>
* <em>Important note:</em> This Maybe is blocking on the thread it gets subscribed on; you cannot dispose it.
* <dl>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code fromFuture} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
*
* @param future
* the source {@link Future}
* @param timeout
* the maximum time to wait before calling {@code get}
* @param unit
* the {@link TimeUnit} of the {@code timeout} argument
* @param <T>
* the type of object that the {@link Future} returns, and also the type of item to be emitted by
* the resulting Maybe
* @return a Maybe that emits the item from the source {@link Future}
* @see <a href="http://reactivex.io/documentation/operators/from.html">ReactiveX operators documentation: From</a>
*/
@CheckReturnValue
@NonNull
@SchedulerSupport(SchedulerSupport.NONE)
public static <T> Maybe<T> fromFuture(Future<? extends T> future, long timeout, TimeUnit unit) {
ObjectHelper.requireNonNull(future, "future is null");
ObjectHelper.requireNonNull(unit, "unit is null");
return RxJavaPlugins.onAssembly(new MaybeFromFuture<T>(future, timeout, unit));
}
/**
* Returns a Maybe instance that runs the given Action for each subscriber and
* emits either its exception or simply completes.
* <dl>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code fromRunnable} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
* @param <T> the target type
* @param run the runnable to run for each subscriber
* @return the new Maybe instance
* @throws NullPointerException if run is null
*/
@CheckReturnValue
@NonNull
@SchedulerSupport(SchedulerSupport.NONE)
public static <T> Maybe<T> fromRunnable(final Runnable run) {
ObjectHelper.requireNonNull(run, "run is null");
return RxJavaPlugins.onAssembly(new MaybeFromRunnable<T>(run));
}
/**
* Returns a {@link Maybe} that invokes the given {@link Supplier} for each individual {@link MaybeObserver} that
* subscribes and emits the resulting non-null item via {@code onSuccess} while
* considering a {@code null} result from the {@code Supplier} as indication for valueless completion
* via {@code onComplete}.
* <p>
* This operator allows you to defer the execution of the given {@code Supplier} until a {@code MaybeObserver}
* subscribes to the returned {@link Maybe}. In other terms, this source operator evaluates the given
* {@code Supplier} "lazily".
* <p>
* <img width="640" height="311" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Maybe.fromSupplier.png" alt="">
* <p>
* Note that the {@code null} handling of this operator differs from the similar source operators in the other
* {@link io.reactivex base reactive classes}. Those operators signal a {@code NullPointerException} if the value returned by their
* {@code Supplier} is {@code null} while this {@code fromSupplier} considers it to indicate the
* returned {@code Maybe} is empty.
* <dl>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code fromSupplier} does not operate by default on a particular {@link Scheduler}.</dd>
* <dt><b>Error handling:</b></dt>
* <dd>Any non-fatal exception thrown by {@link Supplier#get()} will be forwarded to {@code onError},
* except if the {@code MaybeObserver} disposed the subscription in the meantime. In this latter case,
* the exception is forwarded to the global error handler via
* {@link io.reactivex.plugins.RxJavaPlugins#onError(Throwable)} wrapped into a
* {@link io.reactivex.exceptions.UndeliverableException UndeliverableException}.
* Fatal exceptions are rethrown and usually will end up in the executing thread's
* {@link java.lang.Thread.UncaughtExceptionHandler#uncaughtException(Thread, Throwable)} handler.</dd>
* </dl>
*
* @param supplier
* a {@link Supplier} instance whose execution should be deferred and performed for each individual
* {@code MaybeObserver} that subscribes to the returned {@link Maybe}.
* @param <T>
* the type of the item emitted by the {@link Maybe}.
* @return a new Maybe instance
* @see #defer(Supplier)
* @see #fromCallable(Callable)
* @since 3.0.0
*/
@CheckReturnValue
@NonNull
@SchedulerSupport(SchedulerSupport.NONE)
public static <T> Maybe<T> fromSupplier(@NonNull final Supplier<? extends T> supplier) {
ObjectHelper.requireNonNull(supplier, "supplier is null");
return RxJavaPlugins.onAssembly(new MaybeFromSupplier<T>(supplier));
}
/**
* Returns a {@code Maybe} that emits a specified item.
* <p>
* <img width="640" height="485" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Maybe.just.png" alt="">
* <p>
* To convert any object into a {@code Maybe} that emits that object, pass that object into the
* {@code just} method.
* <dl>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code just} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
*
* @param item
* the item to emit
* @param <T>
* the type of that item
* @return a {@code Maybe} that emits {@code item}
* @see <a href="http://reactivex.io/documentation/operators/just.html">ReactiveX operators documentation: Just</a>
*/
@CheckReturnValue
@NonNull
@SchedulerSupport(SchedulerSupport.NONE)
public static <T> Maybe<T> just(T item) {
ObjectHelper.requireNonNull(item, "item is null");
return RxJavaPlugins.onAssembly(new MaybeJust<T>(item));
}
/**
* Merges an Iterable sequence of MaybeSource instances into a single Flowable sequence,
* running all MaybeSources at once.
* <dl>
* <dt><b>Backpressure:</b></dt>
* <dd>The operator honors backpressure from downstream.</dd>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code merge} does not operate by default on a particular {@link Scheduler}.</dd>
* <dt><b>Error handling:</b></dt>
* <dd>If any of the source {@code MaybeSource}s signal a {@code Throwable} via {@code onError}, the resulting
* {@code Flowable} terminates with that {@code Throwable} and all other source {@code MaybeSource}s are disposed.
* If more than one {@code MaybeSource} signals an error, the resulting {@code Flowable} may terminate with the
* first one's error or, depending on the concurrency of the sources, may terminate with a
* {@code CompositeException} containing two or more of the various error signals.
* {@code Throwable}s that didn't make into the composite will be sent (individually) to the global error handler via
* {@link RxJavaPlugins#onError(Throwable)} method as {@code UndeliverableException} errors. Similarly, {@code Throwable}s
* signaled by source(s) after the returned {@code Flowable} has been cancelled or terminated with a
* (composite) error will be sent to the same global error handler.
* Use {@link #mergeDelayError(Iterable)} to merge sources and terminate only when all source {@code MaybeSource}s
* have completed or failed with an error.
* </dd>
* </dl>
* @param <T> the common and resulting value type
* @param sources the Iterable sequence of MaybeSource sources
* @return the new Flowable instance
* @see #mergeDelayError(Iterable)
*/
@BackpressureSupport(BackpressureKind.FULL)
@CheckReturnValue
@SchedulerSupport(SchedulerSupport.NONE)
public static <T> Flowable<T> merge(Iterable<? extends MaybeSource<? extends T>> sources) {
return merge(Flowable.fromIterable(sources));
}
/**
* Merges a Flowable sequence of MaybeSource instances into a single Flowable sequence,
* running all MaybeSources at once.
* <dl>
* <dt><b>Backpressure:</b></dt>
* <dd>The operator honors backpressure from downstream.</dd>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code merge} does not operate by default on a particular {@link Scheduler}.</dd>
* <dt><b>Error handling:</b></dt>
* <dd>If any of the source {@code MaybeSource}s signal a {@code Throwable} via {@code onError}, the resulting
* {@code Flowable} terminates with that {@code Throwable} and all other source {@code MaybeSource}s are disposed.
* If more than one {@code MaybeSource} signals an error, the resulting {@code Flowable} may terminate with the
* first one's error or, depending on the concurrency of the sources, may terminate with a
* {@code CompositeException} containing two or more of the various error signals.
* {@code Throwable}s that didn't make into the composite will be sent (individually) to the global error handler via
* {@link RxJavaPlugins#onError(Throwable)} method as {@code UndeliverableException} errors. Similarly, {@code Throwable}s
* signaled by source(s) after the returned {@code Flowable} has been cancelled or terminated with a
* (composite) error will be sent to the same global error handler.
* Use {@link #mergeDelayError(Publisher)} to merge sources and terminate only when all source {@code MaybeSource}s
* have completed or failed with an error.
* </dd>
* </dl>
* @param <T> the common and resulting value type