工厂方法模式实现，客户端需要决定实例化哪一个工厂来实现运算类，选择判断的问题还是存在的，也就是说，工厂方法把简单工厂的内部逻辑判断移到了客户端来进行，你想加功能，本来是改工厂类，现在是修改客户端。
完整示例
结构图
抽象对象类
Class PHA.YX.Design.Factory.Computer Extends %RegisteredObject
{
Method Create() [ Abstract ]
{
}
Method Install() [ Abstract ]
{
}
}
实例对象类
Class PHA.YX.Design.Factory.HPComputer Extends Computer
{
Method Create()
{
w "创建了HP电脑",!
}
Method Install()
{
w "安装了HP电脑",!
}
}
Class PHA.YX.Design.Factory.LenovoComputer Extends Computer
{
Method Create()
{
w "创建了Lenovo电脑",!
}
Method Install()
{
w "安装了Lenovo电脑",!
}
}
抽象工厂类
Class PHA.YX.Design.Factory.IFactory [ Abstract ]
{
ClassMethod CreateComputer() As Computer [ Abstract ]
{
}
}
实例工厂类
Class PHA.YX.Design.Factory.HPFactory Extends (%RegisteredObject, IFactory)
{
ClassMethod CreateComputer() As Computer
{
qclass(HPComputer).%New()
}
}
Class PHA.YX.Design.Factory.LenovoFactory Extends (%RegisteredObject, IFactory)
{
ClassMethod CreateComputer() As Computer
{
qclass(LenovoComputer).%New()
}
}
调用
/// dclass(PHA.YX.Design.Program).Factory()
ClassMethod Factory()
{
#dim factory as PHA.YX.Design.Factory.IFactory
s factory =class(PHA.YX.Design.Factory.HPFactory).%New()
#dim hpComputer as PHA.YX.Design.Factory.Computer
s hpComputer = factory.CreateComputer()
d hpComputer.Create()
d hpComputer.Install()
s factory =class(PHA.YX.Design.Factory.LenovoFactory).%New()
#dim lenovoComputer as PHA.YX.Design.Factory.Computer
s lenovoComputer = factory.CreateComputer()
d lenovoComputer.Create()
d lenovoComputer.Install()
}
DHC-APP> dclass(PHA.YX.Design.Program).Factory()
创建了HP电脑
安装了HP电脑
创建了Lenovo电脑
安装了Lenovo电脑
思考
用第一章的计算案例，来改写成工厂模式。感兴趣的同学实现后可以发我一起参考下。