工厂方法模式,就是使一个类的实例化延迟到子类——惰性声明
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工厂方法模式无处不在,创建型模式都是依赖于工厂模式的。
简单工厂Simple Factory,这是工厂方法模式的一个特例,因为该模式是通过switch分支(也有用if判断的),来决定最终生成哪一个对象的,而这个switch分支语句,嵌在一个静态方法中,这个改装就是简单工厂。
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在Client端,只要使用 CreateA.CreateAFactory(1).Do(); 就可以生成需要的对象
简单工厂的缺点是,一旦增加新产品类,同时要实现抽象类中的所有方法;还有,一旦要修改抽象类中的方法,所有子类都要变动——扩展性差,不符合开闭原则。
另外,简单工厂模式通常使用静态工厂方法,这使得无法由子类继承,造成工厂角色无法形成基于继承的等级结构。