If not already completed, completes this CompletableFuture with
a {@link CancellationException}. Dependent CompletableFutures
that have not already completed will also complete
exceptionally, with a {@link CompletionException} caused by
this {@code CancellationException}.
@param mayInterruptIfRunning this value has no effect in this
implementation because interrupts are not used to control
processing.
@return {@code true} if this task is now cancelled
If not already completed, completes this CompletableFuture with a {@link CancellationException}. Dependent CompletableFutures that have not already completed will also complete exceptionally, with a {@link CompletionException} caused by this {@code CancellationException}.
@param mayInterruptIfRunning this value has no effect in this implementation because interrupts are not used to control processing.
@return {@code true} if this task is now cancelled