泛型转化的问题

[startray]

inface

public interface aa
{
int test(Entity);
}

class:

public clasee bb:aa
{
public int test(Entity en)
{...操作;return 1;}
}

public classfactory
{
static getclass(){}
}

public testclass1()
{
aa abc = (aa)classfactory.getclass();
aa abc = classfactory.getclass()<aa>;?不用以前的那种转换法。怎么做呢
//这儿要修改为泛型表示，怎么修改呀？那个类里的方法需要修改？
}

[bloodish]

public class classfactory
{
    static T getclass<T>() where T : aa
    {
        //todo
        //return default(T);  
    }
}

[wuyq11]

public interface IBaseDAL<T> where T : BaseModel, new()
{
int Add(T model);
int Update(T model);
int Delete(T model);
}

IBaseDAL<News> newsDAL = factory.GetDAL<News>();