@org.apache.thrift.annotation.Nullable
    public static _Fields findByThriftId(int fieldId) {
      switch(fieldId) {
        case 1: // START_ROW
          return START_ROW;
        case 2: // STOP_ROW
          return STOP_ROW;
        case 3: // COLUMNS
          return COLUMNS;
        case 4: // CACHING
          return CACHING;
        case 5: // MAX_VERSIONS
          return MAX_VERSIONS;
        case 6: // TIME_RANGE
          return TIME_RANGE;
        case 7: // FILTER_STRING
          return FILTER_STRING;
        case 8: // BATCH_SIZE
          return BATCH_SIZE;
        case 9: // ATTRIBUTES
          return ATTRIBUTES;
        case 10: // AUTHORIZATIONS
          return AUTHORIZATIONS;
        case 11: // REVERSED
          return REVERSED;
        case 12: // CACHE_BLOCKS
          return CACHE_BLOCKS;
        case 13: // COL_FAM_TIME_RANGE_MAP
          return COL_FAM_TIME_RANGE_MAP;
        case 14: // READ_TYPE
          return READ_TYPE;
        case 15: // LIMIT
          return LIMIT;
        case 16: // CONSISTENCY
          return CONSISTENCY;
        case 17: // TARGET_REPLICA_ID
          return TARGET_REPLICA_ID;
        case 18: // FILTER_BYTES
          return FILTER_BYTES;
        default:
          return null;
      }
    }
Find the _Fields constant that matches fieldId, or null if its not found.
hbase-thrift/src/main/java/org/apache/hadoop/hbase/thrift2/generated/TScan.java