*/
    protected Maps(final Map<K, V> map) {
        this.map = map;
    }

    /**
     * {@link Map}にキーと値を追加します。
     *
     * @param key
     *            <code>Map</code>に追加されるキー
     * @param value
     *            <code>Map</code>に追加される値
     * @return このインスタンス自身
     */
    public Maps<K, V> $(final K key, final V value) {
        map.put(key, value);
        return this;

      implements MapDifference<K, V> {
    final Map<K, V> onlyOnLeft;
    final Map<K, V> onlyOnRight;
    final Map<K, V> onBoth;
    final Map<K, ValueDifference<V>> differences;

    MapDifferenceImpl(
        Map<K, V> onlyOnLeft,
        Map<K, V> onlyOnRight,
        Map<K, V> onBoth,
        Map<K, ValueDifference<V>> differences) {
      this.onlyOnLeft = unmodifiableMap(onlyOnLeft);

    TreeMap<Integer, Integer> map = Maps.newTreeMap(SOME_COMPARATOR);
    assertEquals(Collections.emptyMap(), map);
    assertSame(SOME_COMPARATOR, map.comparator());
  }

  public void testTreeMapWithInitialMap() {
    SortedMap<Integer, Integer> map = Maps.newTreeMap();
    map.put(5, 10);
    map.put(3, 20);
    map.put(1, 30);
    TreeMap<Integer, Integer> copy = Maps.newTreeMap(map);
    assertEquals(copy, map);

    TreeMap<Integer, Integer> map = Maps.newTreeMap(SOME_COMPARATOR);
    assertEquals(Collections.emptyMap(), map);
    assertSame(SOME_COMPARATOR, map.comparator());
  }

  public void testTreeMapWithInitialMap() {
    SortedMap<Integer, Integer> map = Maps.newTreeMap();
    map.put(5, 10);
    map.put(3, 20);
    map.put(1, 30);
    TreeMap<Integer, Integer> copy = Maps.newTreeMap(map);
    assertEquals(copy, map);

    Map<String, Integer> equalToUnderlying = Maps.newTreeMap();
    equalToUnderlying.putAll(underlying);
    Map<String, Integer> map =
        Maps.transformValues(equalToUnderlying, Functions.<Integer>identity());
    assertMapsEqual(expected, map);

    map =
        Maps.transformValues(
            ImmutableMap.of("a", 1, "b", 2, "c", 3),
            new Function<Integer, Integer>() {

    assertEquals("1", map.remove("a"));
    assertNull(map.remove("b"));
  }

  public void testTransformEqualityOfMapsWithNullValues() {
    Map<String, @Nullable String> underlying = Maps.newHashMap();
    underlying.put("a", null);
    underlying.put("b", "");

    Map<String, Boolean> map =
        Maps.transformValues(
            underlying,

                  @Override
                  protected Map<String, String> create(Entry<String, String>[] entries) {
                    Map<String, String> map = Maps.newHashMap();
                    putEntries(map, entries);
                    map.putAll(ENTRIES_TO_FILTER);
                    map = Maps.filterEntries(map, FILTER_ENTRIES_1);
                    return Maps.filterEntries(map, FILTER_ENTRIES_2);
                  }

    assertEquals("1", map.remove("a"));
    assertNull(map.remove("b"));
  }

  public void testTransformEqualityOfMapsWithNullValues() {
    Map<String, @Nullable String> underlying = Maps.newHashMap();
    underlying.put("a", null);
    underlying.put("b", "");

    Map<String, Boolean> map =
        Maps.transformValues(
            underlying,

                  @Override
                  protected Map<String, String> create(Entry<String, String>[] entries) {
                    Map<String, String> map = Maps.newHashMap();
                    putEntries(map, entries);
                    map.putAll(ENTRIES_TO_FILTER);
                    map = Maps.filterEntries(map, FILTER_ENTRIES_1);
                    return Maps.filterEntries(map, FILTER_ENTRIES_2);
                  }

    assertEquals(Maps.immutableEntry("foo", 5), entryIterator.next());
    assertEquals(Maps.immutableEntry("bar", 4), entryIterator.next());
    assertEquals(Maps.immutableEntry("foo", 3), entryIterator.next());
    assertEquals(Maps.immutableEntry("cow", 2), entryIterator.next());
    assertEquals(Maps.immutableEntry("bar", 1), entryIterator.next());