T - the value typepublic final class AsyncSubject<T> extends Subject<T>
This subject does not have a public constructor by design; a new empty instance of this
AsyncSubject can be created via the create() method.
Since a Subject is conceptionally derived from the Processor type in the Reactive Streams specification,
nulls are not allowed (Rule 2.13)
as parameters to onNext(Object) and onError(Throwable). Such calls will result in a
NullPointerException being thrown and the subject's state is not changed.
Since an AsyncSubject is an Observable, it does not support backpressure.
When this AsyncSubject is terminated via onError(Throwable), the
last observed item (if any) is cleared and late Observers only receive
the onError event.
The AsyncSubject caches the latest item internally and it emits this item only when onComplete is called.
Therefore, it is not recommended to use this Subject with infinite or never-completing sources.
Even though AsyncSubject implements the Observer interface, calling
onSubscribe is not required (Rule 2.12)
if the subject is used as a standalone source. However, calling onSubscribe
after the AsyncSubject reached its terminal state will result in the
given Disposable being disposed immediately.
Calling onNext(Object), onError(Throwable) and onComplete()
is required to be serialized (called from the same thread or called non-overlappingly from different threads
through external means of serialization). The Subject.toSerialized() method available to all Subjects
provides such serialization and also protects against reentrance (i.e., when a downstream Observer
consuming this subject also wants to call onNext(Object) on this subject recursively).
The implementation of onXXX methods are technically thread-safe but non-serialized calls
to them may lead to undefined state in the currently subscribed Observers.
This AsyncSubject supports the standard state-peeking methods hasComplete(), hasThrowable(),
getThrowable() and hasObservers() as well as means to read the very last observed value -
after this AsyncSubject has been completed - in a non-blocking and thread-safe
manner via hasValue() or getValue().
AsyncSubject does not operate by default on a particular Scheduler and
the Observers get notified on the thread where the terminating onError or onComplete
methods were invoked.onError(Throwable) is called, the AsyncSubject enters into a terminal state
and emits the same Throwable instance to the last set of Observers. During this emission,
if one or more Observers dispose their respective Disposables, the
Throwable is delivered to the global error handler via
RxJavaPlugins.onError(Throwable) (multiple times if multiple Observers
cancel at once).
If there were no Observers subscribed to this AsyncSubject when the onError()
was called, the global error handler is not invoked.
Example usage:
AsyncSubject<Object> subject = AsyncSubject.create();
TestObserver<Object> to1 = subject.test();
to1.assertEmpty();
subject.onNext(1);
// AsyncSubject only emits when onComplete was called.
to1.assertEmpty();
subject.onNext(2);
subject.onComplete();
// onComplete triggers the emission of the last cached item and the onComplete event.
to1.assertResult(2);
TestObserver<Object> to2 = subject.test();
// late Observers receive the last cached item too
to2.assertResult(2);
| Modifier and Type | Method and Description |
|---|---|
static <T> @NonNull AsyncSubject<T> |
create ()
Creates a new AsyncProcessor.
|
Throwable |
getThrowable ()
Returns the error that caused the Subject to terminate or null if the Subject
hasn't terminated yet.
|
T |
getValue ()
Returns a single value the Subject currently has or null if no such value exists.
|
boolean |
hasComplete ()
Returns true if the subject has reached a terminal state through a complete event.
|
boolean |
hasObservers ()
Returns true if the subject has any Observers.
|
boolean |
hasThrowable ()
Returns true if the subject has reached a terminal state through an error event.
|
boolean |
hasValue ()
Returns true if the subject has any value.
|
void |
onComplete ()
Notifies the
Observer that the Observable has finished sending push-based notifications. |
void |
onError (Throwable t)
Notifies the
Observer that the Observable has experienced an error condition. |
void |
onNext (T t)
Provides the
Observer with a new item to observe. |
void |
onSubscribe (Disposable d)
Provides the
Observer with the means of cancelling (disposing) the
connection (channel) with the Observable in both
synchronous (from within Observer.onNext(Object)) and asynchronous manner. |
protected void |
subscribeActual (Observer<? super T> observer)
Operator implementations (both source and intermediate) should implement this method that
performs the necessary business logic and handles the incoming
Observers. |
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T - the value type to be received and emittedpublic void onSubscribe(Disposable d)
Observer Observer with the means of cancelling (disposing) the
connection (channel) with the Observable in both
synchronous (from within Observer.onNext(Object)) and asynchronous manner.d - the Disposable instance whose Disposable.dispose() can
be called anytime to cancel the connectionpublic void onNext(T t)
Observer Observer with a new item to observe.
The Observable may call this method 0 or more times.
The Observable will not call this method again after it calls either Observer.onComplete() or
Observer.onError(java.lang.Throwable).
t - the item emitted by the Observablepublic void onError(Throwable t)
Observer Observer that the Observable has experienced an error condition.
If the Observable calls this method, it will not thereafter call Observer.onNext(T) or
Observer.onComplete().
t - the exception encountered by the Observablepublic void onComplete()
Observer Observer that the Observable has finished sending push-based notifications.
The Observable will not call this method if it calls Observer.onError(java.lang.Throwable).
@CheckReturnValue public boolean hasObservers()
Subject The method is thread-safe.
hasObservers in class Subject<T>@CheckReturnValue public boolean hasThrowable()
Subject The method is thread-safe.
hasThrowable in class Subject<T>Subject.getThrowable(),
Subject.hasComplete() @CheckReturnValue public boolean hasComplete()
Subject The method is thread-safe.
hasComplete in class Subject<T>Subject.hasThrowable() @CheckReturnValue public Throwable getThrowable()
Subject The method is thread-safe.
getThrowable in class Subject<T>protected void subscribeActual(Observer<? super T> observer)
Observable Observers.
There is no need to call any of the plugin hooks on the current Observable instance or
the Observer; all hooks and basic safeguards have been
applied by Observable.subscribe(Observer) before this method gets called.
subscribeActual in class Observable<T>observer - the incoming Observer, never null@CheckReturnValue public boolean hasValue()
The method is thread-safe.
@Nullable @CheckReturnValue public T getValue()
The method is thread-safe.