Chen Jian

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来自:http://blog.csdn.net/ericzhong83/article/details/7604728

工厂方法模式(Factory Method Pattern):

定义了一个创建对象的接口,但由子类决定要实例化类的哪一个;即通过子类来创建对象。

原则:

要依赖抽象,不要依赖具体类。

案例:

先解释什么是工厂:
如果你开一家Pizza店(PizzaStore抽象类)卖各种风味的Pizza(Pizza子类),那么你需要根据客户要求准备相应的Pizza(创建Pizza对象),然后烘烤、切片、包装;
最简单的做法就是在PizzaStore中根据客户要求(类型判断)创建相应的Pizza对象,然后调用Pizza自身(由Pizza抽象类实现)的烘烤、切片和包装方法;
但这样的代码缺乏弹性,因为你让一个抽象类去依赖具体的对象;我们可以创建一个工厂来生产Pizza,根据传入的不同类型值返回不同Pizza对象,即从PizzaStore中将创建对象的代码挪到工厂中。但这只是一个编程技巧,并不算模式。

在工厂方法模式中,我们在PizzaStore中定义一个抽象接口(create_pizza)作为抽象的工厂,而order_pizza是它的客户;将Pizza对象的创建放到PizzaStore子类去解决。

现有Cheese和Clam两款Pizza,以及NY和Chicago两家分店,每家店的同款Pizza的口味不同——为迎合当地口味做了改进,主要差别来自不同的原材料,因此我们实现四个Pizza类型(NYStyleCheesePizza、NYStyleClamPizza、 ChicagoStyleCheesePizza和ChicagoStyleClamPizza),每种使用不同的原材料组合,根据客户所在城市和选择款式我们创建不同的对象;根据工厂方法,我们将对象创建的代码放到PizzaStore子类去实现。

代码:

#!/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

输出:

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.
posted on 2015-02-06 08:59  Chen Jian  阅读(208)  评论(0编辑  收藏  举报