@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: // TIMESTAMP
          return TIMESTAMP;
        case 4: // COLUMNS
          return COLUMNS;
        case 5: // CACHING
          return CACHING;
        case 6: // FILTER_STRING
          return FILTER_STRING;
        case 7: // BATCH_SIZE
          return BATCH_SIZE;
        case 8: // SORT_COLUMNS
          return SORT_COLUMNS;
        case 9: // REVERSED
          return REVERSED;
        case 10: // CACHE_BLOCKS
          return CACHE_BLOCKS;
        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/thrift/generated/TScan.java