assertEquals(
        HashCode.fromBytes(mac.doFinal("!!!".getBytes(UTF_8))),
        hmacSha1(SHA1_KEY)
            .newHasher()
            .putString("hello", UTF_8)
            .putString("world", UTF_8)
            .putString("!!!", UTF_8)
            .hash());
  }

  public void testCustomKey() throws Exception {
    SecretKey customKey =
        new SecretKey() {
          @Override

    }

    @CanIgnoreReturnValue
    @Override
    public Hasher putChar(char c) {
      update(2, c);
      return this;
    }

    @CanIgnoreReturnValue
    @Override
    public Hasher putString(CharSequence input, Charset charset) {
      if (charset.equals(UTF_8)) {
        int utf16Length = input.length();
        int i = 0;

        // This loop optimizes for pure ASCII.

   * hashUnencodedChars}.
   *
   * @since 15.0 (since 11.0 as hashString(CharSequence)).
   */
  HashCode hashUnencodedChars(CharSequence input);

  /**
   * Shortcut for {@code newHasher().putString(input, charset).hash()}. Characters are encoded using
   * the given {@link Charset}. The implementation <i>might</i> perform better than its longhand
   * equivalent, but should not perform worse.
   *

        hashFunction.newHasher().putUnencodedChars(string).hash());
    for (Charset charset : CHARSETS) {
      assertEquals(
          hashFunction.hashString(string, charset),
          hashFunction.newHasher().putString(string, charset).hash());
    }
  }

  /**
   * This verifies that putUnencodedChars(String) and hashUnencodedChars(String) are equivalent,

        end = srcIndex + this.rDataLength;
        /*
         * Apparently readRDataWireFormat can return 0 if resultCode != 0 in
         * which case this will look indefinitely. Putting this else clause around
         * the loop might fix that. But I would need to see a capture to confirm.
         * if (resultCode != 0) {
         * srcIndex += rDataLength;
         * } else {
         */

        addrEntry = new NbtAddress[rDataLength / 6];
        end = srcIndex + rDataLength;
        /* Apparently readRDataWireFormat can return 0 if resultCode != 0 in
        which case this will look indefinitely. Putting this else clause around
        the loop might fix that. But I would need to see a capture to confirm.
        if (resultCode != 0) {
            srcIndex += rDataLength;
        } else {
        */

  for (i in 0 until length) {
    val c = this[i]
    if (c <= '\u001f' || c >= '\u007f') {
      return i
    }
  }
  return -1
}

/** Returns true if we should void putting this this header in an exception or toString(). */
internal fun isSensitiveHeader(name: String): Boolean =
  name.equals("Authorization", ignoreCase = true) ||
    name.equals("Cookie", ignoreCase = true) ||

    EntryComparator(@Nullable Comparator<? super K> keyComparator) {
      this.keyComparator = keyComparator;
    }

    @Override
    @SuppressWarnings("unchecked") // no less safe than putting it in the map!
    public int compare(Entry<K, V> a, Entry<K, V> b) {
      return (keyComparator == null)
          ? ((Comparable) a.getKey()).compareTo(b.getKey())
          : keyComparator.compare(a.getKey(), b.getKey());

You will see a lot more of all this in practice in the [Tutorial - User Guide](tutorial/index.md).

## Type Hints with Metadata Annotations { #type-hints-with-metadata-annotations }

Python also has a feature that allows putting **additional <dfn title="Data about the data, in this case, information about the type, e.g. a description.">metadata</dfn>** in these type hints using `Annotated`.

You can import `Annotated` from `typing`.

    @SuppressWarnings("SynchronizeOnNonFinalField")
    public T get() {
      // Another variant of Double Checked Locking.
      //
      // We use two volatile reads. We could reduce this to one by
      // putting our fields into a holder class, but (at least on x86)
      // the extra memory consumption and indirection are more
      // expensive than the extra volatile reads.
      long nanos = expirationNanos;