JAVA的泛型怎么会报错的?

ExaminationPojo dbRes = examinationMapper.selectById(id);

GenerateResCode2 res = new GenerateResCode2<ExaminationPojo>();
res.setRes(dbRes);

//这里会报错的
//Required type: ExaminationPojo
//Provided: Object
ExaminationPojo item = res.getRes();

//用强转换倒是可以，或者定义为object也行，但是用这两个方法泛型不就没意义了吗
//ExaminationPojo item = (ExaminationPojo) res.getRes();
//Object item = res.getRes();

//这个是定义类
public class GenerateResCode2 <T>  {
  private T res;

  public T getRes() {
    return res;
  }

  public void setRes(T res) {
    this.res = res;
  }
}