* {@snippet :
 *        h
 *      / | \
 *     /  e  \
 *    d       g
 *   /|\      |
 *  / | \     f
 * a  b  c
 * }
 *
 * <p>can be iterated over in preorder (hdabcegf), postorder (abcdefgh), or breadth-first order
 * (hdegabcf).
 *
 * <p>Null nodes are strictly forbidden.
 *
 * <p>Because this is an abstract class, not an interface, you can't use a lambda expression to
 * implement it:
 *
 * {@snippet :

     * your current SDK version but also at the oldest version you support. For example, <a
     * href="https://developer.android.com/sdk/api_diff/16/">API Level 16</a> is the first version
     * in which {@code Cursor} is {@code Closeable}. To support older versions, pass a wrapper
     * {@code Closeable} with a method reference like {@code cursor::close}.
     *

    return version
  }

  val javaVersion = System.getProperty("java.version")
  val match = "1\\.8\\.0_(\\d+)(-.*)?".toRegex().find(javaVersion) ?: return null

  return alpnBootVersionForPatchVersion(match.groupValues.first().toInt())

# Request Forms and Files { #request-forms-and-files }

You can define files and form fields at the same time using `File` and `Form`.

/// info

To receive uploaded files and/or form data, first install <a href="https://github.com/Kludex/python-multipart" class="external-link" target="_blank">`python-multipart`</a>.

Make sure you create a [virtual environment](../virtual-environments.md){.internal-link target=_blank}, activate it, and then install it, for example:

  private var isControlFrame = false
  private var readingCompressedMessage = false

  private val controlFrameBuffer = Buffer()
  private val messageFrameBuffer = Buffer()

  /** Lazily initialized on first use. */
  private var messageInflater: MessageInflater? = null

  // Masks are only a concern for server writers.
  private val maskKey: ByteArray? = if (isClient) null else ByteArray(4)

        // Create a defensive copy to avoid ConcurrentModificationException
        List<CommonServerMessageBlock> operationsCopy = List.copyOf(pendingOps);

        // Clear the failed channel's pending operations first
        failedChannel.clearPendingOperations();

        // Redistribute to healthy channels
        for (CommonServerMessageBlock op : operationsCopy) {
            try {

    @Keep public static final WithPublicConstants FIRST = new WithPublicConstants();

    // To test that we pick the first constant alphabetically
    @Keep public static final WithPublicConstants SECOND = new WithPublicConstants();
  }

  private static class FirstConstantIsNull {
    // To test that null constant is ignored
    @Keep public static final @Nullable FirstConstantIsNull FIRST = null;

  private static File file(String first, String... more) {
    return file(new File(first), more);
  }

  /** Returns a {@code File} object for the given path parts. */
  private static File file(File first, String... more) {
    // not very efficient, but should definitely be correct
    File file = first;
    for (String name : more) {
      file = new File(file, name);
    }

# Form Models { #form-models }

You can use **Pydantic models** to declare **form fields** in FastAPI.

/// info

To use forms, first install <a href="https://github.com/Kludex/python-multipart" class="external-link" target="_blank">`python-multipart`</a>.

Make sure you create a [virtual environment](../virtual-environments.md){.internal-link target=_blank}, activate it, and then install it, for example:

```console
$ pip install python-multipart
```

    E[] array = createSamplesArray();
    array[getNumElements() / 2] = e0();
    collection = getSubjectGenerator().create(array);
    assertEquals(
        "indexOf(duplicate) should return index of first occurrence", 0, getList().indexOf(e0()));
  }