設計模式:工廠方法模式(Python)
阿新 • • 發佈:2019-01-07
工廠方法模式(Factory Method Pattern):
定義了一個建立物件的介面,但由子類決定要例項化類的哪一個;即通過子類來建立物件。
原則:
要依賴抽象,不要依賴具體類。
案例:
先解釋什麼是工廠:
如果你開一家Pizza店(PizzaStore抽象類)賣各種風味的Pizza(Pizza子類),那麼你需要根據客戶要求準備相應的Pizza(建立Pizza物件),然後烘烤、切片、包裝;
最簡單的做法就是在PizzaStore中根據客戶要求(型別判斷)建立相應的Pizza物件,然後呼叫Pizza自身(由Pizza抽象類實現)的烘烤、切片和包裝方法;
但這樣的程式碼缺乏彈性,因為你讓一個抽象類去依賴具體的物件;我們可以建立一個工廠來生產Pizza,根據傳入的不同型別值返回不同Pizza物件,即從PizzaStore中將建立物件的程式碼挪到工廠中。但這只是一個程式設計技巧,並不算模式。
在工廠方法模式中,我們在PizzaStore中定義一個抽象介面(create_pizza)作為抽象的工廠,而order_pizza是它的客戶;將Pizza物件的建立放到PizzaStore子類去解決。
現有Cheese和Clam兩款Pizza,以及NY和Chicago兩家分店,每家店的同款Pizza的口味不同——為迎合當地口味做了改進,主要差別來自不同的原材料,因此我們實現四個Pizza型別(NYStyleCheesePizza、NYStyleClamPizza、ChicagoStyleCheesePizza和ChicagoStyleClamPizza),每種使用不同的原材料組合,根據客戶所在城市和選擇款式我們建立不同的物件;根據工廠方法,我們將物件建立的程式碼放到PizzaStore子類去實現。
程式碼:
#!/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
輸出:
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.