code: public <K, V> ConcurrentMap<K, V> makeMap() {
          return useCustomMap ? new StrategyImpl<K, V>(this).map : new ConcurrentHashMap<K, V>(
                  builder.getInitialCapacity(), 0.75f, builder.getConcurrencyLevel());
      }
docs: Builds the final map, without on-demand computation of values. This
  method does not alter the state of this {@code MapMaker} instance, so it
  can be invoked again to create multiple independent maps.
  
  @param <K>
  the type of keys to be stored in the returned map
  @param <V>
  the type of values to be stored in the returned map
  @return a concurrent map having the requested features