@Override
    public void add(int index, E element) {
      synchronized (mutex) {
        delegate().add(index, element);
      }
    }

    @Override
    public boolean addAll(int index, Collection<? extends E> c) {
      synchronized (mutex) {
        return delegate().addAll(index, c);
      }
    }

    @Override
    public E get(int index) {
      synchronized (mutex) {

    private static final String META_NAME_ROBOTS_CONTENT = "//META[@name=\"robots\" or @name=\"ROBOTS\"]/@content";

    /** Robots tag value indicating no indexing or following */
    private static final String ROBOTS_TAG_NONE = "none";

    /** Robots tag value indicating no indexing */
    private static final String ROBOTS_TAG_NOINDEX = "noindex";

    /** Robots tag value indicating no following of links */

                if (userAgent != null) {
                    if (userAgent.indexOf("MSIE") >= 0 || userAgent.indexOf("Trident") >= 0) {
                        uaType = UserAgentType.IE;
                    } else if (userAgent.indexOf("Firefox") >= 0) {
                        uaType = UserAgentType.FIREFOX;
                    } else if (userAgent.indexOf("Chrome") >= 0) {
                        uaType = UserAgentType.CHROME;

        assertThat(ArrayUtil.indexOf(array, "222"), is(1));
        assertThat(ArrayUtil.indexOf(array, "222", 2), is(3));
        assertThat(ArrayUtil.indexOf(array, new Object()), is(-1));
        assertThat(ArrayUtil.indexOf(array, null), is(-1));
        array[1] = null;
        assertThat(ArrayUtil.indexOf(array, null), is(1));
    }

    /**
     * @throws Exception
     */

  public void testIndexOf() {
    assertThat(Shorts.indexOf(EMPTY, (short) 1)).isEqualTo(-1);
    assertThat(Shorts.indexOf(ARRAY1, (short) 2)).isEqualTo(-1);
    assertThat(Shorts.indexOf(ARRAY234, (short) 1)).isEqualTo(-1);
    assertThat(Shorts.indexOf(new short[] {(short) -1}, (short) -1)).isEqualTo(0);
    assertThat(Shorts.indexOf(ARRAY234, (short) 2)).isEqualTo(0);
    assertThat(Shorts.indexOf(ARRAY234, (short) 3)).isEqualTo(1);

    assertThat(iia.indexOf(1)).isEqualTo(0);
    assertThat(iia.indexOf(8)).isEqualTo(5);
    assertThat(iia.indexOf(4)).isEqualTo(-1);
    assertThat(ImmutableDoubleArray.of(13).indexOf(13)).isEqualTo(0);
    assertThat(ImmutableDoubleArray.of().indexOf(21)).isEqualTo(-1);
    assertThat(iia.subArray(1, 5).indexOf(1)).isEqualTo(0);
  }

  public void testIndexOf_specialValues() {

        String result = original;

        // Unquote
        if (result.indexOf('\"') >= 0) {
            final Matcher m = QUOTE_REPLACE_PATTERN.matcher(original);
            if (m.matches()) {
                result = m.group(1);
            }

            // Unescape
            if (result.indexOf(ESCAPED_QUOTE) >= 0) {
                result = result.replace(ESCAPED_QUOTE, "\"");
            }

        AtomicReferenceArray<E> table = this.table;
        int index = hash & (table.length() - 1);
        E first = table.get(index);

        for (E e = first; e != null; e = e.getNext()) {
          if (e == entry) {
            ++modCount;
            E newFirst = removeFromChain(first, e);
            newCount = this.count - 1;
            table.set(index, newFirst);
            this.count = newCount; // write-volatile

            final int indexOf = field.indexOf(':');
            if (indexOf < 0) {
                return new Pair<>(field, null);
            }
            final String indexField = indexOf == 0 ? defaultField : field.substring(0, indexOf);
            final String extensionKey = field.substring(indexOf + 1);
            return new Pair<>(indexField, extensionKey);
        }
    }

  }

  public void testIndexOf() {
    assertThat(Booleans.indexOf(EMPTY, ARRAY_FALSE)).isEqualTo(-1);
    assertThat(Booleans.indexOf(ARRAY_FALSE, ARRAY_FALSE_TRUE)).isEqualTo(-1);
    assertThat(Booleans.indexOf(ARRAY_FALSE_FALSE, ARRAY_FALSE)).isEqualTo(0);
    assertThat(Booleans.indexOf(ARRAY_FALSE, ARRAY_FALSE)).isEqualTo(0);
    assertThat(Booleans.indexOf(ARRAY_FALSE_TRUE, ARRAY_FALSE)).isEqualTo(0);