checkNotNull(a);
    checkNotNull(b);

    int maxPrefixLength = Math.min(a.length(), b.length());
    int p = 0;
    while (p < maxPrefixLength && a.charAt(p) == b.charAt(p)) {
      p++;
    }
    if (validSurrogatePairAt(a, p - 1) || validSurrogatePairAt(b, p - 1)) {
      p--;
    }
    return a.subSequence(0, p).toString();
  }

  /**

    if (s1 == s2) {
      return true;
    }
    if (length != s2.length()) {
      return false;
    }
    for (int i = 0; i < length; i++) {
      char c1 = s1.charAt(i);
      char c2 = s2.charAt(i);
      if (c1 == c2) {
        continue;
      }
      int alphaIndex = getAlphaIndex(c1);
      // This was also benchmarked using '&' to avoid branching (but always evaluate the rhs),

    }
  }

  private static class DontStringMeBro implements CharSequence {
    @Override
    public int length() {
      return 3;
    }

    @Override
    public char charAt(int index) {
      return "foo".charAt(index);
    }

    @Override
    public CharSequence subSequence(int start, int end) {
      return "foo".subSequence(start, end);
    }

    @Override

   *
   * <pre>{@code
   * static final Multimap<Character, String> FIRST_LETTER_MULTIMAP =
   *     Stream.of("banana", "apple", "carrot", "asparagus", "cherry")
   *         .collect(toImmutableSetMultimap(str -> str.charAt(0), str -> str.substring(1)));
   *
   * // is equivalent to
   *
   * static final Multimap<Character, String> FIRST_LETTER_MULTIMAP =
   *     new ImmutableSetMultimap.Builder<Character, String>()

      if (isNullOrEmpty(value)) {
        throw new IllegalArgumentException("value of key " + key + " omitted");
      }
      try {
        char lastChar = value.charAt(value.length() - 1);
        TimeUnit timeUnit;
        switch (lastChar) {
          case 'd':
            timeUnit = TimeUnit.DAYS;
            break;
          case 'h':

        if (utf8Length != Utf8.encodedLength(sb)) {
          StringBuilder repro = new StringBuilder();
          for (int j = 0; j < sb.length(); j++) {
            repro.append(" ").append((int) sb.charAt(j)); // GWT compatible
          }
          assertEquals(repro.toString(), utf8Length, Utf8.encodedLength(sb));
        }
      }
    }
  }

  public void testEncodedLength_invalidStrings() {

    for (String edge : edges) {
      checkArgument(
          edge.length() == 2, "Expecting each edge to consist of 2 characters but got %s", edge);
      char node1 = edge.charAt(0);
      char node2 = edge.charAt(1);
      graphMapBuilder.put(node1, node2);
      if (!directed) {
        graphMapBuilder.put(node2, node1);
      }
    }

  public void testFlatteningToImmutableListMultimap() {
    Collector<String, ?, ImmutableListMultimap<Character, Character>> collector =
        ImmutableListMultimap.flatteningToImmutableListMultimap(
            str -> str.charAt(0), str -> Chars.asList(str.substring(1).toCharArray()).stream());
    BiPredicate<Multimap<?, ?>, Multimap<?, ?>> equivalence =
        Equivalence.equals()

      new Function<@Nullable String, @Nullable Character>() {
        @Override
        public @Nullable Character apply(@Nullable String input) {
          return input == null ? null : input.charAt(0);
        }
      };

  abstract static class ColumnMapTests extends MapMapTests {
    ColumnMapTests(
        boolean allowsNullValues,
        boolean supportsRemove,
        boolean supportsClear,

  @Generates
  Byte generateByteObject() {
    return new Byte(generateByte());
  }

  @Generates
  char generateChar() {
    return generateString().charAt(0);
  }

  @SuppressWarnings("removal") // b/321209431 -- maybe just use valueOf here?
  @Generates
  Character generateCharacter() {
    return new Character(generateChar());
  }

  @Generates