实例讲解Python设计模式编程之工厂方法模式的使用
工厂方法模式是简单工厂模式的进一步抽象和推广,它不仅保持了简单工厂模式能够向客户隐藏类的实例化过程这一优点,而且还通过多态性克服了工厂类过于复杂且不易于扩展的缺点。在工厂方法模式中,处于核心地位的工厂类不再负责所有产品的创建,而是将具体的创建工作交由子类去完成。工厂方法模式中的核心工厂类经过功能抽象之后,成为了一个抽象的工厂角色,仅负责给出具体工厂子类必须实现的接口,而不涉及哪种产品类应当被实例化这一细节。工厂方法模式的一般性结构如下图所示,图中为了简化只给出了一个产品类和一个工厂类,但在实际系统中通常需要设计多个产品类和多个工厂类。 工厂方法模式的实质是将对象的创建延迟到其子类实现,即由子类根据当前情况动态决定应该实例化哪一个产品类。从上图可以看出,工厂方法模式涉及到抽象工厂角色、具体工厂角色、抽象产品角色和具体产品角色四个参与者。
抽象工厂角色负责声明工厂方法(factory method),用来"生产"抽象产品,以下是抽象工厂的示例性Python代码: creator.py # 创建抽象产品的工厂方法 def factoryMethod(self): pass 具体工厂角色负责创建一个具体产品的实例,并将其返回给调用者。具体工厂是与具体产品相关的,实现时一般常用的做法是为每个具体产品定义一个具体工厂。以下是具体工厂的示例性Python代码: # 创建具体产品的工厂方法 def factoryMethod(self): product = ConcreteProduct() return product 抽象产品角色的主要目的是为所有的具体产品提供一个共同的接口,通常只需给出相应的声明就可以了,而不用给出具体的实现。以下是抽象产品类的示例性Python代码: # 所有产品类的公共接口 def interface(self): pass 具体产品角色充当最终的创建目标,一般来讲它是抽象产品类的子类,实现了抽象产品类中定义的所有工厂方法,实际应用时通常会具有比较复杂的业务逻辑。以下是具体产品类的示例性Python代码: # 公共接口的实现 def interface(self): print "Concrete Product Method" def run(self): creator = ConcreteCreator() product = creator.factoryMethod() product.interface() # 主函数 if (__name__ == "__main__"): client = Client() client.run()
下面我们来看一个具体案例: #!/usr/bin/python class Pizza: name = "" dough = "" sauce = "" toppings = [] def prepare(self): print "Preparing %s" % self.name print " dough: %s" % self.dough print " sauce: %s" % self.sauce print " add toppings:" for n in self.toppings: print " %s" % n def bake(self): print "Bake for 25 minutes at 350." def cut(self): print "Cutting into diagonal slices." def box(self): print "Put into official box." def get_name(self): return self.name class PizzaStore: def order_pizza(self,pizza_type): self.pizza = self.create_pizza(pizza_type) self.pizza.prepare() self.pizza.bake() self.pizza.cut() self.pizza.box() return self.pizza def create_pizza(self,pizza_type): pass class NYStyleCheesePizza(Pizza): def __init__(self): self.name = "NY Style Cheese Pizza" self.dough = "NY Dough" self.sauce = "NY Sauce" self.toppings.append("NY toopping A") self.toppings.append("NY toopping B") class ChicagoStyleCheesePizza(Pizza): def __init__(self): self.name = "Chicago Style Cheese Pizza" self.dough = "Chicago Dough" self.sauce = "Chicago Sauce" sefl.toppings.append("Chicago toopping A") def cut(self): print "Cutting into square slices." class NYStyleClamPizza(Pizza): def __init__(self): self.name = "NY Style Clam Pizza" self.dough = "NY Dough" self.sauce = "NY Sauce" self.toppings.append("NY toopping A") self.toppings.append("NY toopping B") class ChicagoStyleClamPizza(Pizza): def __init__(self): self.name = "Chicago Style Clam Pizza" self.dough = "Chicago Dough" self.sauce = "Chicago Sauce" self.toppings.append("Chicago toopping A") def cut(self): print "Cutting into square slices." class NYPizzaStore(PizzaStore): def create_pizza(self,pizza_type): if pizza_type == "cheese": return NYStyleCheesePizza() elif pizza_type == "clam": return NYStyleClamPizza() else: return None class ChicagoPizzaStore(PizzaStore): def create_pizza(self,pizza_type): if pizza_type == "cheese": return ChicagoStyleCheesePizza() elif pizza_type == "clam": return ChicagoStyleClamPizza() else: return None if __name__ == "__main__": ny_store = NYPizzaStore() chicago_store = ChicagoPizzaStore() pizza = ny_store.order_pizza("cheese") print "Mike ordered a %s." % pizza.get_name() print pizza = chicago_store.order_pizza("clam") print "John ordered a %s." % pizza.get_name() print
Preparing NY Style Cheese Pizza dough: NY Dough sauce: NY Sauce add toppings: NY toopping A NY toopping B Bake for 25 minutes at 350. Cutting into diagonal slices. Put into official box. Mike ordered a NY Style Cheese Pizza. Preparing Chicago Style Clam Pizza dough: Chicago Dough sauce: Chicago Sauce add toppings: NY toopping A NY toopping B Chicago toopping A Bake for 25 minutes at 350. Cutting into square slices. Put into official box. John ordered a Chicago Style Clam Pizza. (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |