Package io.reactivex.rxjava3.subjects

Class PublishSubject<T>

  • Type Parameters:
    T - the type of items observed and emitted by the Subject
    All Implemented Interfaces:
    ObservableSource<T>, Observer<T>
    public final class PublishSubject<T>
extends Subject<T>
    A Subject that emits (multicasts) items to currently subscribed Observers and terminal events to current or late Observers.

    This subject does not have a public constructor by design; a new empty instance of this PublishSubject 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 a PublishSubject is an Observable, it does not support backpressure.

    When this PublishSubject is terminated via onError(Throwable) or onComplete(), late Observers only receive the respective terminal event.

    Unlike a BehaviorSubject, a PublishSubject doesn't retain/cache items, therefore, a new Observer won't receive any past items.

    Even though PublishSubject 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 PublishSubject 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).

    This PublishSubject supports the standard state-peeking methods hasComplete(), hasThrowable(), getThrowable() and hasObservers().

    Scheduler:
    PublishSubject does not operate by default on a particular Scheduler and the Observers get notified on the thread the respective onXXX methods were invoked.
    Error handling:
    When the onError(Throwable) is called, the PublishSubject 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 PublishSubject when the onError() was called, the global error handler is not invoked.

    Example usage: 

     

  PublishSubject<Object> subject = PublishSubject.create();
  // observer1 will receive all onNext and onComplete events
  subject.subscribe(observer1);
  subject.onNext("one");
  subject.onNext("two");
  // observer2 will only receive "three" and onComplete
  subject.subscribe(observer2);
  subject.onNext("three");
  subject.onComplete();

  // late Observers only receive the terminal event
  subject.test().assertEmpty();

    • Field Detail

      • error

        java.lang.Throwable error
        The error, write before terminating and read after checking subscribers.

    • Constructor Detail

      • PublishSubject

        PublishSubject()
        Constructs a PublishSubject.
        Since:
        2.0

    • Method Detail

      • subscribeActual

        protected void subscribeActual​(Observer<? super T> t)
        Description copied from class: Observable
        Operator implementations (both source and intermediate) should implement this method that performs the necessary business logic and handles the incoming 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.

        Specified by:
        subscribeActual in class Observable<T>
        Parameters:
        t - the incoming Observer, never null

      • add

        boolean add​(PublishSubject.PublishDisposable<T> ps)
        Tries to add the given subscriber to the subscribers array atomically or returns false if the subject has terminated.
        Parameters:
        ps - the subscriber to add
        Returns:
        true if successful, false if the subject has terminated

      • remove

        void remove​(PublishSubject.PublishDisposable<T> ps)
        Atomically removes the given subscriber if it is subscribed to the subject.
        Parameters:
        ps - the subject to remove

      • onError

        public void onError​(java.lang.Throwable t)
        Description copied from interface: Observer
        Notifies the 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().

        Parameters:
        t - the exception encountered by the Observable

      • hasObservers

        @CheckReturnValue
public boolean hasObservers()
        Description copied from class: Subject
        Returns true if the subject has any Observers.

        The method is thread-safe.

        Specified by:
        hasObservers in class Subject<T>
        Returns:
        true if the subject has any Observers

      • getThrowable

        @Nullable
@CheckReturnValue
public @Nullable java.lang.Throwable getThrowable()
        Description copied from class: Subject
        Returns the error that caused the Subject to terminate or null if the Subject hasn't terminated yet.

        The method is thread-safe.

        Specified by:
        getThrowable in class Subject<T>
        Returns:
        the error that caused the Subject to terminate or null if the Subject hasn't terminated yet

      • hasComplete

        @CheckReturnValue
public boolean hasComplete()
        Description copied from class: Subject
        Returns true if the subject has reached a terminal state through a complete event.

        The method is thread-safe.

        Specified by:
        hasComplete in class Subject<T>
        Returns:
        true if the subject has reached a terminal state through a complete event
        See Also:
        Subject.hasThrowable()