Method create

onjava/FillMap.java:27–37

(Supplier<K> keyGen,
           Supplier<V> valueGen,
           Supplier<M> mapSupplier, int size)

        .toMap(Pair::key, Pair::value));
  }
  public static <K, V, M extends Map<K,V>>
  M create(Supplier<K> keyGen,
           Supplier<V> valueGen,
           Supplier<M> mapSupplier, int size) {
    return Stream.generate( () ->
      Pair.make(keyGen.get(), valueGen.get()))
        .limit(size)
        .collect(Collectors
          .toMap(Pair::key, Pair::value,
                 (k, v) -> k, mapSupplier));
  }
}