public String apply(String input) {
          return new String(BaseEncoding.base64().decode(input), UTF_8);
        }
      };

  private static final EntryTransformer<String, String, String> DECODE_ENTRY_TRANSFORMER =
      new EntryTransformer<String, String, String>() {
        @Override
        public String transformEntry(String key, String value) {
          return DECODE_FUNCTION.apply(value);
        }

  }

  public void testTransformEntries() {
    Map<String, String> map = ImmutableMap.of("a", "4", "b", "9");
    EntryTransformer<String, String, String> concat =
        new EntryTransformer<String, String, String>() {
          @Override
          public String transformEntry(String key, String value) {
            return key + value;
          }
        };

          @Override
          public String apply(String value) {
            return Ascii.toLowerCase(value);
          }
        };

    static final EntryTransformer<String, String, String> ENTRY_TRANSFORMER =
        new EntryTransformer<String, String, String>() {
          @Override
          public String transformEntry(String key, String value) {
            return Ascii.toLowerCase(value);
          }

   *
   * <p><b>Warning:</b> This method assumes that for any instance {@code k} of {@code
   * EntryTransformer} key type {@code K}, {@code k.equals(k2)} implies that {@code k2} is also of
   * type {@code K}. Using an {@code EntryTransformer} key type for which this may not hold, such as
   * {@code ArrayList}, may risk a {@code ClassCastException} when calling methods on the

   *
   * <p><b>Warning:</b> This method assumes that for any instance {@code k} of {@code
   * EntryTransformer} key type {@code K}, {@code k.equals(k2)} implies that {@code k2} is also of
   * type {@code K}. Using an {@code EntryTransformer} key type for which this may not hold, such as
   * {@code ArrayList}, may risk a {@code ClassCastException} when calling methods on the

   *
   * <p><b>Warning:</b> This method assumes that for any instance {@code k} of {@code
   * EntryTransformer} key type {@code K}, {@code k.equals(k2)} implies that {@code k2} is also of
   * type {@code K}. Using an {@code EntryTransformer} key type for which this may not hold, such as
   * {@code ArrayList}, may risk a {@code ClassCastException} when calling methods on the
   * transformed map.

  }

  @GwtIncompatible // untested
  public void testTransformEntries() {
    SetMultimap<String, Integer> multimap = ImmutableSetMultimap.of("a", 1, "a", 4, "b", -6);
    EntryTransformer<String, Integer, String> transformer =
        new EntryTransformer<String, Integer, String>() {
          @Override
          public String transformEntry(String key, Integer value) {
            return (value >= 0) ? key : "no" + key;
          }

   *
   * <p><b>Warning:</b> This method assumes that for any instance {@code k} of {@code
   * EntryTransformer} key type {@code K}, {@code k.equals(k2)} implies that {@code k2} is also of
   * type {@code K}. Using an {@code EntryTransformer} key type for which this may not hold, such as
   * {@code ArrayList}, may risk a {@code ClassCastException} when calling methods on the
   * transformed map.

          @Override
          public String apply(String value) {
            return Ascii.toLowerCase(value);
          }
        };

    static final EntryTransformer<String, String, String> ENTRY_TRANSFORMER =
        new EntryTransformer<String, String, String>() {
          @Override
          public String transformEntry(String key, String value) {
            return Ascii.toLowerCase(value);
          }