public boolean isSet(_Fields field) {
    if (field == null) {
      throw new java.lang.IllegalArgumentException();
    }

    switch (field) {
    case REGION_NAME:
      return isSetRegionName();
    case CLIENT_ADDRESS:
      return isSetClientAddress();
    case TABLE_NAME:
      return isSetTableName();
    case USER_NAME:
      return isSetUserName();
    case LIMIT:
      return isSetLimit();
    case LOG_TYPE:
      return isSetLogType();
    case FILTER_BY_OPERATOR:
      return isSetFilterByOperator();
    }
    throw new java.lang.IllegalStateException();
  }
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/TLogQueryFilter.java