Numeric (and accumulators)

[Brian Goetz]

> One reason for integrating into j.u.c is that keyed versions of
> these forms would need to generalize what is now LongAdderTable

How much better (pick your metrics) is the keyed form of LAT than a CHM 
of Accumulators?

> /**
>   * Example: Maps from keys to Accumulators can be used to create
> Histograms
>   * (frequency maps) and related tables.
>   *
>   * To increment a count, installing if not already present:
>   *  map.computeIfAbsent(key, () ->
> LongAccumulator.optimisticSum()).update(1L);
>   *
>   * To determine the sum for a key, it is convenient to create a
>   * singleton static EMPTY_ACCUMULATOR, enabling
>   *   long sum = map.getValueOrDefault(key, EMPTY_ACCUMULATOR).get();
>   */
>
> Any thoughts on this?

Like it.  Does that mean we don't need LAT at all?