@Override
  public int hashCode() {
    return (((this.first == null ? 1 : this.first.hashCode()) * 17)
      + (this.second == null ? 1 : this.second.hashCode()) * 19);
  }
@param f First element in pair.
@param s Second element in pair.
hcatalog/core/src/main/java/org/apache/hive/hcatalog/data/Pair.java