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 {@link CompletionStage} documentation for rules
covering exceptional completion.
@param other the other CompletionStage
@param fn the function to use to compute the value of the
returned CompletionStage
@param (U) the function's return type
@return the new CompletionStage
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 {@link CompletionStage} documentation for rules covering exceptional completion.
@param other the other CompletionStage @param fn the function to use to compute the value of the returned CompletionStage @param (U) the function's return type @return the new CompletionStage