@org.apache.thrift.annotation.Nullable
    public static _Fields findByThriftId(int fieldId) {
      switch(fieldId) {
        case 1: // AINT
          return AINT;
        case 2: // A_STRING
          return A_STRING;
        case 3: // LINT
          return LINT;
        case 4: // L_STRING
          return L_STRING;
        case 5: // LINT_STRING
          return LINT_STRING;
        case 6: // M_STRING_STRING
          return M_STRING_STRING;
        case 7: // ATTRIBUTES
          return ATTRIBUTES;
        case 8: // UNION_FIELD1
          return UNION_FIELD1;
        case 9: // UNION_FIELD2
          return UNION_FIELD2;
        case 10: // UNION_FIELD3
          return UNION_FIELD3;
        default:
          return null;
      }
    }
Find the _Fields constant that matches fieldId, or null if its not found.
serde/src/gen/thrift/gen-javabean/org/apache/hadoop/hive/serde2/thrift/test/Complex.java