code: @SuppressWarnings("unchecked")
    public boolean contains(final Object key) {
      // validate key
      if (key == null) {
        throw new IllegalArgumentException("Null element is not supported.");
      }
      // find element
      final int hashCode = ((T)key).hashCode();
      final int index = getIndex(hashCode);
      return containsElem(index, (T) key, hashCode);
    }
docs: Check if the set contains given element
  
  @return true if element present, false otherwise.