code: public Database change_db_obj(final String host, final String port) throws DevFailed {
          // Get requested database object
          final Database dbase = get_db_obj(host, port);
          // And set it at first vector element as default Dbase
          db_list.remove(dbase);
          db_list.add(0, dbase);
          defaultDatabase = dbase;
          return dbase;
      }
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