public int indexOf(Object o) {
    synchronized (lock) {
      int currentSize = size();
      if (o == null) {
        for (int i = 0; i < currentSize; i++) {
          if (elementData[i] == null) {
            return i;
          }
        }
      } else {
        for (int i = 0; i < currentSize; i++) {
          if (o.equals(elementData[i])) {
            return i;
          }
        }
      }
    }
    return -1;
  }
Returns the index of the first occurrence of the specified element in this list, or -1 if this
list does not contain the element. More formally, returns the lowest index <tt>i</tt> such that
<tt>(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i)))</tt>, or -1 if there is no
such index.
geode-core/src/main/java/org/apache/geode/cache/query/internal/index/IndexElemArray.java