Parent variable = new Child();

public class ReportBuilder {
   public ReportBuilder() {
   }

   public createReport(Report report) {
      data = report.collectData();
      excelFile = this.makeExcel(report, report.template());
      this.publishAndSave(excelFile);
   }
}

abstract class Report {
   DataContainer collectData();
   String template()
}

class ReportA extends Report {
   DataContainer collectData() {
      // собираем одни данные
   }

   String template() {
      return 'file1.xls';
   }
}

class ReportB extends Report {
   DataContainer collectData() {
      // собираем одни данные
   }

   String template() {
      return 'file1.xls';
   }
}

reportBuilder = new ReportBuilder();
reportBuilder.createReport(new ReportA());
reportBuilder.createReport(new ReportB());

class Child {
   private int age;

   @Override
   String toString() {
      return "age is "+age;
   }
}


Child child=new Child();
Object myObject=child;
System.out.println(child);  //печатаем объект Child
System.out.println(myObject);  //печатаем объект Object