code: protected String[] getAllowedCommands(String classname) {
          try {
              DeviceData argin = new DeviceData();
              argin.insert(classname);
              DeviceData argout = command_inout("GetAllowedCommands", argin);
              String[] allowed = argout.extractStringArray();
              allowed_cmd_table.put(classname, allowed);
              return allowed;
          } catch (DevFailed e) {
              String[] dummy = new String[0];
              allowed_cmd_table.put(classname, dummy);
              return dummy;
          }
      }
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