Class PublishSubject<T>

java.lang.Object
io.reactivex.rxjava4.core.Observable<T>
io.reactivex.rxjava4.subjects.Subject<T>
io.reactivex.rxjava4.subjects.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();

  • Method Details

    • create

      @CheckReturnValue @NonNull public static <T> @NonNull PublishSubject<T> create()
      Constructs a PublishSubject.
      Type Parameters:
      T - the value type
      Returns:
      the new PublishSubject

    • 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

    • onSubscribe

      public void onSubscribe(Disposable d)
      Description copied from interface: Observer
      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.
      Parameters:
      d - the Disposable instance whose Disposable.dispose() can be called anytime to cancel the connection

    • onNext

      public void onNext(T t)
      Description copied from interface: Observer
      Provides the 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(Throwable).

      Parameters:
      t - the item emitted by the Observable

    • onError

      public void onError(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

    • onComplete

      public void onComplete()
      Description copied from interface: Observer
      Notifies the Observer that the Observable has finished sending push-based notifications.

      The Observable will not call this method if it calls Observer.onError(Throwable).

    • 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 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

    • hasThrowable

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

      The method is thread-safe.

      Specified by:
      hasThrowable in class Subject<T>
      Returns:
      true if the subject has reached a terminal state through an error event
      See Also:

    • 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: