unfiltered.put("apple", 2);
    unfiltered.put("banana", 6);
    unfiltered.put("cat", 3);
    unfiltered.put("dog", 5);

    SortedMap<String, Integer> filtered = Maps.filterEntries(unfiltered, CORRECT_LENGTH);
    assertEquals("banana", filtered.firstKey());
    assertEquals("cat", filtered.lastKey());
  }

  public void testHeadSubTailMap_FilteredMap() {

  protected Map<String, Map<Integer, Character>> makePopulatedMap() {
    Table<Integer, String, String> table = HashBasedTable.create();
    table.put(1, "foo", "apple");
    table.put(1, "bar", "banana");
    table.put(3, "foo", "cat");
    return Tables.transformValues(table, FIRST_CHARACTER).columnMap();
  }

          Tables.immutableCell("bar", 1, 'a'),
          Tables.immutableCell("bar", 2, 'b'),
          Tables.immutableCell("foo", 3, 'c'),
          Tables.immutableCell("bar", 1, 'b'),
          Tables.immutableCell("cat", 2, 'b'));
    }

    @Override
    public Set<Cell<String, Integer, Character>> create(Object... elements) {
      Table<String, Integer, Character> table = createTable();
      for (Object element : elements) {

    ms.add("b");
    ms.add("c");

    assertEquals(2, ms.count("bar"));
    assertEquals(3, ms.count("b"));

    Multiset<String> ms2 = TreeMultiset.create(DEGENERATE_COMPARATOR);

    ms2.add("cat", 2);
    ms2.add("x", 3);

    assertEquals(ms, ms2);
    assertEquals(ms2, ms);

    SortedSet<String> elementSet = ms.elementSet();
    assertEquals("a", elementSet.first());

  }

  // use an enum to get easy serializability
  private enum CharAtFunction implements Function<String, Character> {
    AT0(0),
    AT1(1),
    AT2(2),
    AT3(3),
    AT4(4),
    AT5(5),
    ;

    final int index;

    CharAtFunction(int index) {
      this.index = index;
    }

    @Override
    public Character apply(String string) {

  }

  // use an enum to get easy serializability
  private enum CharAtFunction implements Function<String, Character> {
    AT0(0),
    AT1(1),
    AT2(2),
    AT3(3),
    AT4(4),
    AT5(5),
    ;

    final int index;

    CharAtFunction(int index) {
      this.index = index;
    }

    @Override
    public Character apply(String string) {

   * the beginning and from the end of the string. For example:
   *
   * <pre>{@code
   * CharMatcher.anyOf("ab").trimFrom("abacatbab")
   * }</pre>
   *
   * ... returns {@code "cat"}.
   *
   * <p>Note that:
   *
   * <pre>{@code
   * CharMatcher.inRange('\0', ' ').trimFrom(str)
   * }</pre>
   *
   * ... is equivalent to {@link String#trim()}.
   */

    } catch (NullPointerException expected) {
    }
    try {
      table.put("cat", null, cellValue('d'));
      fail();
    } catch (NullPointerException expected) {
    }
    if (supportsNullValues()) {
      assertNull(table.put("cat", 2, null));
      assertTrue(table.contains("cat", 2));
    } else {
      try {
        table.put("cat", 2, null);
        fail();
      } catch (NullPointerException expected) {
      }

    table.put("foo", 4, 'a');
    table.put("cat", 1, 'b');
    table.clear();
    populate(table, data);
    return table;
  }

  @Override
  protected TreeBasedTable<String, Integer, Character> create(@Nullable Object... data) {
    TreeBasedTable<String, Integer, Character> table = TreeBasedTable.create();
    table.put("foo", 4, 'a');
    table.put("cat", 1, 'b');
    table.clear();
    populate(table, data);

    table = create("foo", 1, 'a', "bar", 1, 'b', "foo", 3, 'c');
    Table<String, Integer, Character> other = HashBasedTable.create();
    other.put("foo", 1, 'd');
    other.put("bar", 2, 'e');
    other.put("cat", 2, 'f');
    try {
      table.putAll(other);
      fail("Expected UnsupportedOperationException");
    } catch (UnsupportedOperationException expected) {
    }
    assertEquals((Character) 'a', table.get("foo", 1));