* EntryTransformer<String, Boolean, String> flagPrefixer =
   *     new EntryTransformer<String, Boolean, String>() {
   *       public String transformEntry(String key, Boolean value) {
   *         return value ? key : "yes" + key;
   *       }
   *     };
   * SortedMap<String, String> transformed =
   *     Maps.transformEntries(options, flagPrefixer);
   * System.out.println(transformed);
   * }</pre>
   *