* </ul>
 *
 * <p>
 * The class uses synchronization to ensure thread safety when accessing and modifying the URL queue.
 * It also checks for duplicate URLs before adding them to the queue,
 * both within the queue itself and against previously accessed URLs stored in the {@link MemoryDataHelper}.
 * </p>
 *
 */
/**
 * This class is an implementation of {@link UrlQueueService}.
 */

Then we can declare `tags` as a set of strings:

{* ../../docs_src/body_nested_models/tutorial003_py310.py hl[12] *}

With this, even if you receive a request with duplicate data, it will be converted to a set of unique items.

And whenever you output that data, even if the source had duplicates, it will be output as a set of unique items.

And it will be annotated / documented accordingly too.

## Nested Models { #nested-models }

import java.util.SortedSet;
import org.jspecify.annotations.Nullable;

/**
 * A {@code SetMultimap} whose set of values for a given key are kept sorted; that is, they comprise
 * a {@link SortedSet}. It cannot hold duplicate key-value pairs; adding a key-value pair that's
 * already in the multimap has no effect. This interface does not specify the ordering of the

    }

    @Override
    public Set<E> create(Object... elements) {
      Object[] duplicated = new Object[elements.length * 2];
      for (int i = 0; i < elements.length; i++) {
        duplicated[i] = elements[i];
        duplicated[i + elements.length] = elements[i];
      }
      return ((Multiset<E>) gen.create(duplicated)).elementSet();
    }

    @Override
    public E[] createArray(int length) {

    E[] array = (E[]) elements.toArray();
    /*
     * For a Set, we guess that it contains no duplicates. That's just a guess for purpose of
     * sizing; if the Set uses different equality semantics, it might contain duplicates according
     * to equals(), and we will deduplicate those properly, albeit at some cost in allocations.
     */
    int expectedSize =

                    new ContentNotFoundException(urlQueue.getParentUrl(), url));
        }
    }

    /**
     * Stores a child URL in the crawling queue with duplicate host handling.
     * This method applies duplicate host conversion before storing the URL.
     *
     * @param childUrl the child URL to store
     * @param parentUrl the parent URL that referenced this child URL

    // my best guess is that the jdk authors have spent more time optimizing that callpath than this
    // one. (StringCoding$StringDecoder vs. StreamDecoder).  StringCoding has a ton of special cases
    // theoretically we could duplicate all that logic here to try to beat 'new String' or at least
    // come close.
    USING_DECODER_WITH_SIZE_HINT {
      @Override
      String read(ByteSource byteSource, Charset cs) throws IOException {

          else -> readToken()
        } ?: return // Expected a value.

      val replaced = parameters.put(peek, parameterValue)
      peek = null
      if (replaced != null) return // Unexpected duplicate parameter.
      if (!skipCommasAndWhitespace() && !exhausted()) return // Expected ',' or EOF.
    }
    result.add(Challenge(schemeName, parameters))
  }
}

/** Returns true if any commas were skipped. */

 *
 * <p>When iterating through the collections supplied by this class, the ordering of values for a
 * given key agrees with the order in which the values were added.
 *
 * <p>This multimap allows duplicate key-value pairs. After adding a new key-value pair equal to an
 * existing key-value pair, the {@code ArrayListMultimap} will contain entries for both the new
 * value and the old value.
 *

            return matcher.group(1);
        }
        return null;
    }

    /**
     * Gets a duplicate URL by adding or removing a trailing slash.
     *
     * @param requestData the request data to create a duplicate for
     * @return the request data with the duplicate URL
     */
    protected RequestData getDuplicateUrl(final RequestData requestData) {
        final String url = requestData.getUrl();