CompletionStage (Java Platform SE 8 )
Keywords: java.util.concurrent.CompletionStage interface
Date: 2016-12-09

compact1, compact2, compact3
java.util.concurrent

## Interface CompletionStage<T>

- All Known Implementing Classes:
    CompletableFuture

      public interface CompletionStage<T>

  A stage of a possibly asynchronous computation, that performs an action or computes a value when another CompletionStage completes. A stage completes upon termination of its computation, but this may in turn trigger other dependent stages. The functionality defined in this interface takes only a few basic forms, which expand out to a larger set of methods to capture a range of usage styles:
  - The computation performed by a stage may be expressed as a Function, Consumer, or Runnable (using methods with names including apply, accept, or run, respectively) depending on whether it requires arguments and/or produces results. For example, `stage.thenApply(x -> square(x)).thenAccept(x -> System.out.print(x)).thenRun(() -> System.out.println())`. An additional form (compose) applies functions of stages themselves, rather than their results.
  - One stage's execution may be triggered by completion of a single stage, or both of two stages, or either of two stages. Dependencies on a single stage are arranged using methods with prefix then. Those triggered by completion of both of two stages may combine their results or effects, using correspondingly named methods. Those triggered by either of two stages make no guarantees about which of the results or effects are used for the dependent stage's computation.
  - Dependencies among stages control the triggering of computations, but do not otherwise guarantee any particular ordering. Additionally, execution of a new stage's computations may be arranged in any of three ways: default execution, default asynchronous execution (using methods with suffix async that employ the stage's default asynchronous execution facility), or custom (via a supplied `Executor`). The execution properties of default and async modes are specified by CompletionStage implementations, not this interface. Methods with explicit Executor arguments may have arbitrary execution properties, and might not even support concurrent execution, but are arranged for processing in a way that accommodates asynchrony.
  - Two method forms support processing whether the triggering stage completed normally or exceptionally: Method `whenComplete` allows injection of an action regardless of outcome, otherwise preserving the outcome in its completion. Method `handle` additionally allows the stage to compute a replacement result that may enable further processing by other dependent stages. In all other cases, if a stage's computation terminates abruptly with an (unchecked) exception or error, then all dependent stages requiring its completion complete exceptionally as well, with a `CompletionException` holding the exception as its cause. If a stage is dependent on both of two stages, and both complete exceptionally, then the CompletionException may correspond to either one of these exceptions. If a stage is dependent on either of two others, and only one of them completes exceptionally, no guarantees are made about whether the dependent stage completes normally or exceptionally. In the case of method `whenComplete`, when the supplied action itself encounters an exception, then the stage exceptionally completes with this exception if not already completed exceptionally.

  All methods adhere to the above triggering, execution, and exceptional completion specifications (which are not repeated in individual method specifications). Additionally, while arguments used to pass a completion result (that is, for parameters of type `T`) for methods accepting them may be null, passing a null value for any other parameter will result in a `NullPointerException` being thrown.

  This interface does not define methods for initially creating, forcibly completing normally or exceptionally, probing completion status or results, or awaiting completion of a stage. Implementations of CompletionStage may provide means of achieving such effects, as appropriate. Method `toCompletableFuture()` enables interoperability among different implementations of this interface by providing a common conversion type.

  Since:
    1.8

- - ### Method Summary

    All Methods Instance Methods Abstract Methods
    Modifier and Type | Method and Description
    --- | ---
    `CompletionStage<Void>` | `acceptEither(CompletionStage<? extends T> other, Consumer<? super T> action)` Returns a new CompletionStage that, when either this or the other given stage complete normally, is executed with the corresponding result as argument to the supplied action.
    `CompletionStage<Void>` | `acceptEitherAsync(CompletionStage<? extends T> other, Consumer<? super T> action)` Returns a new CompletionStage that, when either this or the other given stage complete normally, is executed using this stage's default asynchronous execution facility, with the corresponding result as argument to the supplied action.
    `CompletionStage<Void>` | `acceptEitherAsync(CompletionStage<? extends T> other, Consumer<? super T> action, Executor executor)` Returns a new CompletionStage that, when either this or the other given stage complete normally, is executed using the supplied executor, with the corresponding result as argument to the supplied function.
    `<U> CompletionStage<U>` | `applyToEither(CompletionStage<? extends T> other, Function<? super T,U> fn)` Returns a new CompletionStage that, when either this or the other given stage complete normally, is executed with the corresponding result as argument to the supplied function.
    `<U> CompletionStage<U>` | `applyToEitherAsync(CompletionStage<? extends T> other, Function<? super T,U> fn)` Returns a new CompletionStage that, when either this or the other given stage complete normally, is executed using this stage's default asynchronous execution facility, with the corresponding result as argument to the supplied function.
    `<U> CompletionStage<U>` | `applyToEitherAsync(CompletionStage<? extends T> other, Function<? super T,U> fn, Executor executor)` Returns a new CompletionStage that, when either this or the other given stage complete normally, is executed using the supplied executor, with the corresponding result as argument to the supplied function.
    `CompletionStage<T>` | `exceptionally(Function<Throwable,? extends T> fn)` Returns a new CompletionStage that, when this stage completes exceptionally, is executed with this stage's exception as the argument to the supplied function.
    `<U> CompletionStage<U>` | `handle(BiFunction<? super T,Throwable,? extends U> fn)` Returns a new CompletionStage that, when this stage completes either normally or exceptionally, is executed with this stage's result and exception as arguments to the supplied function.
    `<U> CompletionStage<U>` | `handleAsync(BiFunction<? super T,Throwable,? extends U> fn)` Returns a new CompletionStage that, when this stage completes either normally or exceptionally, is executed using this stage's default asynchronous execution facility, with this stage's result and exception as arguments to the supplied function.
    `<U> CompletionStage<U>` | `handleAsync(BiFunction<? super T,Throwable,? extends U> fn, Executor executor)` Returns a new CompletionStage that, when this stage completes either normally or exceptionally, is executed using the supplied executor, with this stage's result and exception as arguments to the supplied function.
    `CompletionStage<Void>` | `runAfterBoth(CompletionStage<?> other, Runnable action)` Returns a new CompletionStage that, when this and the other given stage both complete normally, executes the given action.
    `CompletionStage<Void>` | `runAfterBothAsync(CompletionStage<?> other, Runnable action)` Returns a new CompletionStage that, when this and the other given stage complete normally, executes the given action using this stage's default asynchronous execution facility.
    `CompletionStage<Void>` | `runAfterBothAsync(CompletionStage<?> other, Runnable action, Executor executor)` Returns a new CompletionStage that, when this and the other given stage complete normally, executes the given action using the supplied executor.
    `CompletionStage<Void>` | `runAfterEither(CompletionStage<?> other, Runnable action)` Returns a new CompletionStage that, when either this or the other given stage complete normally, executes the given action.
    `CompletionStage<Void>` | `runAfterEitherAsync(CompletionStage<?> other, Runnable action)` Returns a new CompletionStage that, when either this or the other given stage complete normally, executes the given action using this stage's default asynchronous execution facility.
    `CompletionStage<Void>` | `runAfterEitherAsync(CompletionStage<?> other, Runnable action, Executor executor)` Returns a new CompletionStage that, when either this or the other given stage complete normally, executes the given action using the supplied executor.
    `CompletionStage<Void>` | `thenAccept(Consumer<? super T> action)` Returns a new CompletionStage that, when this stage completes normally, is executed with this stage's result as the argument to the supplied action.
    `CompletionStage<Void>` | `thenAcceptAsync(Consumer<? super T> action)` Returns a new CompletionStage that, when this stage completes normally, is executed using this stage's default asynchronous execution facility, with this stage's result as the argument to the supplied action.
    `CompletionStage<Void>` | `thenAcceptAsync(Consumer<? super T> action, Executor executor)` Returns a new CompletionStage that, when this stage completes normally, is executed using the supplied Executor, with this stage's result as the argument to the supplied action.
    `<U> CompletionStage<Void>` | `thenAcceptBoth(CompletionStage<? extends U> other, BiConsumer<? super T,? super U> action)` Returns a new CompletionStage that, when this and the other given stage both complete normally, is executed with the two results as arguments to the supplied action.
    `<U> CompletionStage<Void>` | `thenAcceptBothAsync(CompletionStage<? extends U> other, BiConsumer<? super T,? super U> action)` Returns a new CompletionStage that, when this and the other given stage complete normally, is executed using this stage's default asynchronous execution facility, with the two results as arguments to the supplied action.
    `<U> CompletionStage<Void>` | `thenAcceptBothAsync(CompletionStage<? extends U> other, BiConsumer<? super T,? super U> action, Executor executor)` Returns a new CompletionStage that, when this and the other given stage complete normally, is executed using the supplied executor, with the two results as arguments to the supplied function.
    `<U> CompletionStage<U>` | `thenApply(Function<? super T,? extends U> fn)` Returns a new CompletionStage that, when this stage completes normally, is executed with this stage's result as the argument to the supplied function.
    `<U> CompletionStage<U>` | `thenApplyAsync(Function<? super T,? extends U> fn)` Returns a new CompletionStage that, when this stage completes normally, is executed using this stage's default asynchronous execution facility, with this stage's result as the argument to the supplied function.
    `<U> CompletionStage<U>` | `thenApplyAsync(Function<? super T,? extends U> fn, Executor executor)` Returns a new CompletionStage that, when this stage completes normally, is executed using the supplied Executor, with this stage's result as the argument to the supplied function.
    `<U,V> CompletionStage<V>` | `thenCombine(CompletionStage<? extends U> other, BiFunction<? super T,? super U,? extends V> fn)` Returns a new CompletionStage that, when this and the other given stage both complete normally, is executed with the two results as arguments to the supplied function.
    `<U,V> CompletionStage<V>` | `thenCombineAsync(CompletionStage<? extends U> other, BiFunction<? super T,? super U,? extends V> fn)` Returns a new CompletionStage that, when this and the other given stage complete normally, is executed using this stage's default asynchronous execution facility, with the two results as arguments to the supplied function.
    `<U,V> CompletionStage<V>` | `thenCombineAsync(CompletionStage<? extends U> other, BiFunction<? super T,? super U,? extends V> fn, Executor executor)` Returns a new CompletionStage that, when this and the other given stage complete normally, is executed using the supplied executor, with the two results as arguments to the supplied function.
    `<U> CompletionStage<U>` | `thenCompose(Function<? super T,? extends CompletionStage<U>> fn)` Returns a new CompletionStage that, when this stage completes normally, is executed with this stage as the argument to the supplied function.
    `<U> CompletionStage<U>` | `thenComposeAsync(Function<? super T,? extends CompletionStage<U>> fn)` Returns a new CompletionStage that, when this stage completes normally, is executed using this stage's default asynchronous execution facility, with this stage as the argument to the supplied function.
    `<U> CompletionStage<U>` | `thenComposeAsync(Function<? super T,? extends CompletionStage<U>> fn, Executor executor)` Returns a new CompletionStage that, when this stage completes normally, is executed using the supplied Executor, with this stage's result as the argument to the supplied function.
    `CompletionStage<Void>` | `thenRun(Runnable action)` Returns a new CompletionStage that, when this stage completes normally, executes the given action.
    `CompletionStage<Void>` | `thenRunAsync(Runnable action)` Returns a new CompletionStage that, when this stage completes normally, executes the given action using this stage's default asynchronous execution facility.
    `CompletionStage<Void>` | `thenRunAsync(Runnable action, Executor executor)` Returns a new CompletionStage that, when this stage completes normally, executes the given action using the supplied Executor.
    `CompletableFuture<T>` | `toCompletableFuture()` Returns a `CompletableFuture` maintaining the same completion properties as this stage.
    `CompletionStage<T>` | `whenComplete(BiConsumer<? super T,? super Throwable> action)` Returns a new CompletionStage with the same result or exception as this stage, that executes the given action when this stage completes.
    `CompletionStage<T>` | `whenCompleteAsync(BiConsumer<? super T,? super Throwable> action)` Returns a new CompletionStage with the same result or exception as this stage, that executes the given action using this stage's default asynchronous execution facility when this stage completes.
    `CompletionStage<T>` | `whenCompleteAsync(BiConsumer<? super T,? super Throwable> action, Executor executor)` Returns a new CompletionStage with the same result or exception as this stage, that executes the given action using the supplied Executor when this stage completes.

- - ### Method Detail

    - #### thenApply

          <U> CompletionStage<U> thenApply(Function<? super T,? extends U> fn)

      Returns a new CompletionStage that, when this stage completes normally, is executed with this stage's result as the argument to the supplied function. See the `CompletionStage` documentation for rules covering exceptional completion.
      Type Parameters:
        `U` - the function's return type
      Parameters:
        `fn` - the function to use to compute the value of the returned CompletionStage
      Returns:
        the new CompletionStage

    - #### thenApplyAsync

          <U> CompletionStage<U> thenApplyAsync(Function<? super T,? extends U> fn)

      Returns a new CompletionStage that, when this stage completes normally, is executed using this stage's default asynchronous execution facility, with this stage's result as the argument to the supplied function. See the `CompletionStage` documentation for rules covering exceptional completion.
      Type Parameters:
        `U` - the function's return type
      Parameters:
        `fn` - the function to use to compute the value of the returned CompletionStage
      Returns:
        the new CompletionStage

    - #### thenApplyAsync

          <U> CompletionStage<U> thenApplyAsync(Function<? super T,? extends U> fn,
                                                Executor executor)

      Returns a new CompletionStage that, when this stage completes normally, is executed using the supplied Executor, with this stage's result as the argument to the supplied function. See the `CompletionStage` documentation for rules covering exceptional completion.
      Type Parameters:
        `U` - the function's return type
      Parameters:
        `fn` - the function to use to compute the value of the returned CompletionStage
        `executor` - the executor to use for asynchronous execution
      Returns:
        the new CompletionStage

    - #### thenAccept

          CompletionStage<Void> thenAccept(Consumer<? super T> action)

      Returns a new CompletionStage that, when this stage completes normally, is executed with this stage's result as the argument to the supplied action. See the `CompletionStage` documentation for rules covering exceptional completion.
      Parameters:
        `action` - the action to perform before completing the returned CompletionStage
      Returns:
        the new CompletionStage

    - #### thenAcceptAsync

          CompletionStage<Void> thenAcceptAsync(Consumer<? super T> action)

      Returns a new CompletionStage that, when this stage completes normally, is executed using this stage's default asynchronous execution facility, with this stage's result as the argument to the supplied action. See the `CompletionStage` documentation for rules covering exceptional completion.
      Parameters:
        `action` - the action to perform before completing the returned CompletionStage
      Returns:
        the new CompletionStage

    - #### thenAcceptAsync

          CompletionStage<Void> thenAcceptAsync(Consumer<? super T> action,
                                                Executor executor)

      Returns a new CompletionStage that, when this stage completes normally, is executed using the supplied Executor, with this stage's result as the argument to the supplied action. See the `CompletionStage` documentation for rules covering exceptional completion.
      Parameters:
        `action` - the action to perform before completing the returned CompletionStage
        `executor` - the executor to use for asynchronous execution
      Returns:
        the new CompletionStage

    - #### thenRun

          CompletionStage<Void> thenRun(Runnable action)

      Returns a new CompletionStage that, when this stage completes normally, executes the given action. See the `CompletionStage` documentation for rules covering exceptional completion.
      Parameters:
        `action` - the action to perform before completing the returned CompletionStage
      Returns:
        the new CompletionStage

    - #### thenRunAsync

          CompletionStage<Void> thenRunAsync(Runnable action)

      Returns a new CompletionStage that, when this stage completes normally, executes the given action using this stage's default asynchronous execution facility. See the `CompletionStage` documentation for rules covering exceptional completion.
      Parameters:
        `action` - the action to perform before completing the returned CompletionStage
      Returns:
        the new CompletionStage

    - #### thenRunAsync

          CompletionStage<Void> thenRunAsync(Runnable action,
                                             Executor executor)

      Returns a new CompletionStage that, when this stage completes normally, executes the given action using the supplied Executor. See the `CompletionStage` documentation for rules covering exceptional completion.
      Parameters:
        `action` - the action to perform before completing the returned CompletionStage
        `executor` - the executor to use for asynchronous execution
      Returns:
        the new CompletionStage

    - #### thenCombine

          <U,V> CompletionStage<V> thenCombine(CompletionStage<? extends U> other,
                                               BiFunction<? super T,? super U,? extends V> fn)

      Returns a new CompletionStage that, when this and the other given stage both complete normally, is executed with the two results as arguments to the supplied function. See the `CompletionStage` documentation for rules covering exceptional completion.
      Type Parameters:
        `U` - the type of the other CompletionStage's result
        `V` - the function's return type
      Parameters:
        `other` - the other CompletionStage
        `fn` - the function to use to compute the value of the returned CompletionStage
      Returns:
        the new CompletionStage

    - #### thenCombineAsync

          <U,V> CompletionStage<V> thenCombineAsync(CompletionStage<? extends U> other,
                                                    BiFunction<? super T,? super U,? extends V> fn)

      Returns a new CompletionStage that, when this and the other given stage complete normally, is executed using this stage's default asynchronous execution facility, with the two results as arguments to the supplied function. See the `CompletionStage` documentation for rules covering exceptional completion.
      Type Parameters:
        `U` - the type of the other CompletionStage's result
        `V` - the function's return type
      Parameters:
        `other` - the other CompletionStage
        `fn` - the function to use to compute the value of the returned CompletionStage
      Returns:
        the new CompletionStage

    - #### thenCombineAsync

          <U,V> CompletionStage<V> thenCombineAsync(CompletionStage<? extends U> other,
                                                    BiFunction<? super T,? super U,? extends V> fn,
                                                    Executor executor)

      Returns a new CompletionStage that, when this and the other given stage complete normally, is executed using the supplied executor, with the two results as arguments to the supplied function. See the `CompletionStage` documentation for rules covering exceptional completion.
      Type Parameters:
        `U` - the type of the other CompletionStage's result
        `V` - the function's return type
      Parameters:
        `other` - the other CompletionStage
        `fn` - the function to use to compute the value of the returned CompletionStage
        `executor` - the executor to use for asynchronous execution
      Returns:
        the new CompletionStage

    - #### thenAcceptBoth

          <U> CompletionStage<Void> thenAcceptBoth(CompletionStage<? extends U> other,
                                                   BiConsumer<? super T,? super U> action)

      Returns a new CompletionStage that, when this and the other given stage both complete normally, is executed with the two results as arguments to the supplied action. See the `CompletionStage` documentation for rules covering exceptional completion.
      Type Parameters:
        `U` - the type of the other CompletionStage's result
      Parameters:
        `other` - the other CompletionStage
        `action` - the action to perform before completing the returned CompletionStage
      Returns:
        the new CompletionStage

    - #### thenAcceptBothAsync

          <U> CompletionStage<Void> thenAcceptBothAsync(CompletionStage<? extends U> other,
                                                        BiConsumer<? super T,? super U> action)

      Returns a new CompletionStage that, when this and the other given stage complete normally, is executed using this stage's default asynchronous execution facility, with the two results as arguments to the supplied action.
      Type Parameters:
        `U` - the type of the other CompletionStage's result
      Parameters:
        `other` - the other CompletionStage
        `action` - the action to perform before completing the returned CompletionStage
      Returns:
        the new CompletionStage

    - #### thenAcceptBothAsync

          <U> CompletionStage<Void> thenAcceptBothAsync(CompletionStage<? extends U> other,
                                                        BiConsumer<? super T,? super U> action,
                                                        Executor executor)

      Returns a new CompletionStage that, when this and the other given stage complete normally, is executed using the supplied executor, with the two results as arguments to the supplied function.
      Type Parameters:
        `U` - the type of the other CompletionStage's result
      Parameters:
        `other` - the other CompletionStage
        `action` - the action to perform before completing the returned CompletionStage
        `executor` - the executor to use for asynchronous execution
      Returns:
        the new CompletionStage

    - #### runAfterBoth

          CompletionStage<Void> runAfterBoth(CompletionStage<?> other,
                                             Runnable action)

      Returns a new CompletionStage that, when this and the other given stage both complete normally, executes the given action. See the `CompletionStage` documentation for rules covering exceptional completion.
      Parameters:
        `other` - the other CompletionStage
        `action` - the action to perform before completing the returned CompletionStage
      Returns:
        the new CompletionStage

    - #### runAfterBothAsync

          CompletionStage<Void> runAfterBothAsync(CompletionStage<?> other,
                                                  Runnable action)

      Returns a new CompletionStage that, when this and the other given stage complete normally, executes the given action using this stage's default asynchronous execution facility. See the `CompletionStage` documentation for rules covering exceptional completion.
      Parameters:
        `other` - the other CompletionStage
        `action` - the action to perform before completing the returned CompletionStage
      Returns:
        the new CompletionStage

    - #### runAfterBothAsync

          CompletionStage<Void> runAfterBothAsync(CompletionStage<?> other,
                                                  Runnable action,
                                                  Executor executor)

      Returns a new CompletionStage that, when this and the other given stage complete normally, executes the given action using the supplied executor. See the `CompletionStage` documentation for rules covering exceptional completion.
      Parameters:
        `other` - the other CompletionStage
        `action` - the action to perform before completing the returned CompletionStage
        `executor` - the executor to use for asynchronous execution
      Returns:
        the new CompletionStage

    - #### applyToEither

          <U> CompletionStage<U> applyToEither(CompletionStage<? extends T> other,
                                               Function<? super T,U> fn)

      Returns a new CompletionStage that, when either this or the other given stage complete normally, is executed with the corresponding result as argument to the supplied function. See the `CompletionStage` documentation for rules covering exceptional completion.
      Type Parameters:
        `U` - the function's return type
      Parameters:
        `other` - the other CompletionStage
        `fn` - the function to use to compute the value of the returned CompletionStage
      Returns:
        the new CompletionStage

    - #### applyToEitherAsync

          <U> CompletionStage<U> applyToEitherAsync(CompletionStage<? extends T> other,
                                                    Function<? super T,U> fn)

      Returns a new CompletionStage that, when either this or the other given stage complete normally, is executed using this stage's default asynchronous execution facility, with the corresponding result as argument to the supplied function. See the `CompletionStage` documentation for rules covering exceptional completion.
      Type Parameters:
        `U` - the function's return type
      Parameters:
        `other` - the other CompletionStage
        `fn` - the function to use to compute the value of the returned CompletionStage
      Returns:
        the new CompletionStage

    - #### applyToEitherAsync

          <U> CompletionStage<U> applyToEitherAsync(CompletionStage<? extends T> other,
                                                    Function<? super T,U> fn,
                                                    Executor executor)

      Returns a new CompletionStage that, when either this or the other given stage complete normally, is executed using the supplied executor, with the corresponding result as argument to the supplied function. See the `CompletionStage` documentation for rules covering exceptional completion.
      Type Parameters:
        `U` - the function's return type
      Parameters:
        `other` - the other CompletionStage
        `fn` - the function to use to compute the value of the returned CompletionStage
        `executor` - the executor to use for asynchronous execution
      Returns:
        the new CompletionStage

    - #### acceptEither

          CompletionStage<Void> acceptEither(CompletionStage<? extends T> other,
                                             Consumer<? super T> action)

      Returns a new CompletionStage that, when either this or the other given stage complete normally, is executed with the corresponding result as argument to the supplied action. See the `CompletionStage` documentation for rules covering exceptional completion.
      Parameters:
        `other` - the other CompletionStage
        `action` - the action to perform before completing the returned CompletionStage
      Returns:
        the new CompletionStage

    - #### acceptEitherAsync

          CompletionStage<Void> acceptEitherAsync(CompletionStage<? extends T> other,
                                                  Consumer<? super T> action)

      Returns a new CompletionStage that, when either this or the other given stage complete normally, is executed using this stage's default asynchronous execution facility, with the corresponding result as argument to the supplied action. See the `CompletionStage` documentation for rules covering exceptional completion.
      Parameters:
        `other` - the other CompletionStage
        `action` - the action to perform before completing the returned CompletionStage
      Returns:
        the new CompletionStage

    - #### acceptEitherAsync

          CompletionStage<Void> acceptEitherAsync(CompletionStage<? extends T> other,
                                                  Consumer<? super T> action,
                                                  Executor executor)

      Returns a new CompletionStage that, when either this or the other given stage complete normally, is executed using the supplied executor, with the corresponding result as argument to the supplied function. See the `CompletionStage` documentation for rules covering exceptional completion.
      Parameters:
        `other` - the other CompletionStage
        `action` - the action to perform before completing the returned CompletionStage
        `executor` - the executor to use for asynchronous execution
      Returns:
        the new CompletionStage

    - #### runAfterEither

          CompletionStage<Void> runAfterEither(CompletionStage<?> other,
                                               Runnable action)

      Returns a new CompletionStage that, when either this or the other given stage complete normally, executes the given action. See the `CompletionStage` documentation for rules covering exceptional completion.
      Parameters:
        `other` - the other CompletionStage
        `action` - the action to perform before completing the returned CompletionStage
      Returns:
        the new CompletionStage

    - #### runAfterEitherAsync

          CompletionStage<Void> runAfterEitherAsync(CompletionStage<?> other,
                                                    Runnable action)

      Returns a new CompletionStage that, when either this or the other given stage complete normally, executes the given action using this stage's default asynchronous execution facility. See the `CompletionStage` documentation for rules covering exceptional completion.
      Parameters:
        `other` - the other CompletionStage
        `action` - the action to perform before completing the returned CompletionStage
      Returns:
        the new CompletionStage

    - #### runAfterEitherAsync

          CompletionStage<Void> runAfterEitherAsync(CompletionStage<?> other,
                                                    Runnable action,
                                                    Executor executor)

      Returns a new CompletionStage that, when either this or the other given stage complete normally, executes the given action using the supplied executor. See the `CompletionStage` documentation for rules covering exceptional completion.
      Parameters:
        `other` - the other CompletionStage
        `action` - the action to perform before completing the returned CompletionStage
        `executor` - the executor to use for asynchronous execution
      Returns:
        the new CompletionStage

    - #### thenCompose

          <U> CompletionStage<U> thenCompose(Function<? super T,? extends CompletionStage<U>> fn)

      Returns a new CompletionStage that, when this stage completes normally, is executed with this stage as the argument to the supplied function. See the `CompletionStage` documentation for rules covering exceptional completion.
      Type Parameters:
        `U` - the type of the returned CompletionStage's result
      Parameters:
        `fn` - the function returning a new CompletionStage
      Returns:
        the CompletionStage

    - #### thenComposeAsync

          <U> CompletionStage<U> thenComposeAsync(Function<? super T,? extends CompletionStage<U>> fn)

      Returns a new CompletionStage that, when this stage completes normally, is executed using this stage's default asynchronous execution facility, with this stage as the argument to the supplied function. See the `CompletionStage` documentation for rules covering exceptional completion.
      Type Parameters:
        `U` - the type of the returned CompletionStage's result
      Parameters:
        `fn` - the function returning a new CompletionStage
      Returns:
        the CompletionStage

    - #### thenComposeAsync

          <U> CompletionStage<U> thenComposeAsync(Function<? super T,? extends CompletionStage<U>> fn,
                                                  Executor executor)

      Returns a new CompletionStage that, when this stage completes normally, is executed using the supplied Executor, with this stage's result as the argument to the supplied function. See the `CompletionStage` documentation for rules covering exceptional completion.
      Type Parameters:
        `U` - the type of the returned CompletionStage's result
      Parameters:
        `fn` - the function returning a new CompletionStage
        `executor` - the executor to use for asynchronous execution
      Returns:
        the CompletionStage

    - #### exceptionally

          CompletionStage<T> exceptionally(Function<Throwable,? extends T> fn)

      Returns a new CompletionStage that, when this stage completes exceptionally, is executed with this stage's exception as the argument to the supplied function. Otherwise, if this stage completes normally, then the returned stage also completes normally with the same value.
      Parameters:
        `fn` - the function to use to compute the value of the returned CompletionStage if this CompletionStage completed exceptionally
      Returns:
        the new CompletionStage

    - #### whenComplete

          CompletionStage<T> whenComplete(BiConsumer<? super T,? super Throwable> action)

      Returns a new CompletionStage with the same result or exception as this stage, that executes the given action when this stage completes.

      When this stage is complete, the given action is invoked with the result (or `null` if none) and the exception (or `null` if none) of this stage as arguments. The returned stage is completed when the action returns. If the supplied action itself encounters an exception, then the returned stage exceptionally completes with this exception unless this stage also completed exceptionally.

      Parameters:
        `action` - the action to perform
      Returns:
        the new CompletionStage

    - #### whenCompleteAsync

          CompletionStage<T> whenCompleteAsync(BiConsumer<? super T,? super Throwable> action)

      Returns a new CompletionStage with the same result or exception as this stage, that executes the given action using this stage's default asynchronous execution facility when this stage completes.

      When this stage is complete, the given action is invoked with the result (or `null` if none) and the exception (or `null` if none) of this stage as arguments. The returned stage is completed when the action returns. If the supplied action itself encounters an exception, then the returned stage exceptionally completes with this exception unless this stage also completed exceptionally.

      Parameters:
        `action` - the action to perform
      Returns:
        the new CompletionStage

    - #### whenCompleteAsync

          CompletionStage<T> whenCompleteAsync(BiConsumer<? super T,? super Throwable> action,
                                               Executor executor)

      Returns a new CompletionStage with the same result or exception as this stage, that executes the given action using the supplied Executor when this stage completes.

      When this stage is complete, the given action is invoked with the result (or `null` if none) and the exception (or `null` if none) of this stage as arguments. The returned stage is completed when the action returns. If the supplied action itself encounters an exception, then the returned stage exceptionally completes with this exception unless this stage also completed exceptionally.

      Parameters:
        `action` - the action to perform
        `executor` - the executor to use for asynchronous execution
      Returns:
        the new CompletionStage

    - #### handle

          <U> CompletionStage<U> handle(BiFunction<? super T,Throwable,? extends U> fn)

      Returns a new CompletionStage that, when this stage completes either normally or exceptionally, is executed with this stage's result and exception as arguments to the supplied function.

      When this stage is complete, the given function is invoked with the result (or `null` if none) and the exception (or `null` if none) of this stage as arguments, and the function's result is used to complete the returned stage.

      Type Parameters:
        `U` - the function's return type
      Parameters:
        `fn` - the function to use to compute the value of the returned CompletionStage
      Returns:
        the new CompletionStage

    - #### handleAsync

          <U> CompletionStage<U> handleAsync(BiFunction<? super T,Throwable,? extends U> fn)

      Returns a new CompletionStage that, when this stage completes either normally or exceptionally, is executed using this stage's default asynchronous execution facility, with this stage's result and exception as arguments to the supplied function.

      When this stage is complete, the given function is invoked with the result (or `null` if none) and the exception (or `null` if none) of this stage as arguments, and the function's result is used to complete the returned stage.

      Type Parameters:
        `U` - the function's return type
      Parameters:
        `fn` - the function to use to compute the value of the returned CompletionStage
      Returns:
        the new CompletionStage

    - #### handleAsync

          <U> CompletionStage<U> handleAsync(BiFunction<? super T,Throwable,? extends U> fn,
                                             Executor executor)

      Returns a new CompletionStage that, when this stage completes either normally or exceptionally, is executed using the supplied executor, with this stage's result and exception as arguments to the supplied function.

      When this stage is complete, the given function is invoked with the result (or `null` if none) and the exception (or `null` if none) of this stage as arguments, and the function's result is used to complete the returned stage.

      Type Parameters:
        `U` - the function's return type
      Parameters:
        `fn` - the function to use to compute the value of the returned CompletionStage
        `executor` - the executor to use for asynchronous execution
      Returns:
        the new CompletionStage

    - #### toCompletableFuture

          CompletableFuture<T> toCompletableFuture()

      Returns a `CompletableFuture` maintaining the same completion properties as this stage. If this stage is already a CompletableFuture, this method may return this stage itself. Otherwise, invocation of this method may be equivalent in effect to `thenApply(x -> x)`, but returning an instance of type `CompletableFuture`. A CompletionStage implementation that does not choose to interoperate with others may throw `UnsupportedOperationException`.
      Returns:
        the CompletableFuture
      Throws:
        `UnsupportedOperationException` - if this implementation does not interoperate with CompletableFuture

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