@Override
  public int hashCode() {
    int hashCode = 1;

    hashCode = hashCode * 8191 + ((isSetExpression()) ? 131071 : 524287);
    if (isSetExpression())
      hashCode = hashCode * 8191 + expression.hashCode();

    return hashCode;
  }
Returns true if field corresponding to fieldID is set (has been assigned a value) and false otherwise
hbase-thrift/src/main/java/org/apache/hadoop/hbase/thrift2/generated/TCellVisibility.java