設計模式之十--組合模式

組合模式：將對象組合成熟型結構一表示‘部分-整體’的層次結構。組合模式使得用戶對單個對象的組合對象的使用具有一致性。具體來講就是，樹根和樹枝和樹葉都是統一對待的。樹枝和樹葉繼承於樹根。

什麼時候用組合模式？
當需求中是體現部分與整體的層次結構式，以及你希望用戶可以忽略組合對象與單個對象的不同，統一使用組合結構中的所有對象時，就應該考慮用組合模式。好了，上代碼。

from abc import ABCMeta, abstractmethod


class Company(metaclass=ABCMeta):

    def __init__(self, name):
        self.name = name

    @abstractmethod
    def add(self, company):
        pass

    @abstractmethod
    def remove(self, company):
        pass

    @abstractmethod
    def display(self, depth):
        pass

    @abstractmethod
    def line_of_duty(self):
        pass


class ConcreteCompany(Company):

    def __init__(self, name):
        super().__init__(name)
        self.children = []

    def add(self, company):
        self.children.append(company)

    def remove(self, company):
        self.children.remove(company)

    def display(self, depth):
        print('-'*depth + "Company {0}".format(self.name))
        for company in self.children:
            company.display(depth + 2)

    def line_of_duty(self):
        for company in self.children:
            company.line_of_duty()


class HRDepartment(Company):

    def __init__(self, name):
        super().__init__(name)

    def add(self, company):
        pass

    def remove(self, company):
        pass

    def display(self, depth):
        print('-'*depth + self.name)

    def line_of_duty(self):
        print("{0} This department is responsible for recruiting employees".format(self.name))


class FinanceDepartment(Company):

    def __init__(self, name):
        super().__init__(name)

    def add(self, company):
        pass

    def remove(self, company):
        pass

    def display(self, depth):
        print('-'*depth + self.name)

    def line_of_duty(self):
        print("{0} This department is responsible for managing the money".format(self.name))


if __name__ == "__main__":

    headquarter = ConcreteCompany("Headquarter")
    headquarter.add(HRDepartment("Root HR"))
    headquarter.add(FinanceDepartment("Root Finance"))

    south_subsidy = ConcreteCompany("SouthSubsidy")
    south_subsidy.add(HRDepartment("SouthSubsidy HR Department"))
    south_subsidy.add(FinanceDepartment("SouthSubsidy Finance Department"))
    headquarter.add(south_subsidy)

    north_subsidy = ConcreteCompany("NorthSubsidy")
    north_subsidy.add(HRDepartment("NorthSubsidy HR Department"))
    north_subsidy.add(FinanceDepartment("NorthSubsidy Finance Department"))
    headquarter.add(north_subsidy)

    headquarter.display(1)
    headquarter.line_of_duty()

這段代碼中，優點浪費的是，具體的部門類，也就是樹葉，裏邊爲了統一性會有一部分的代碼沒有實現。也可以把這些去掉。在Comany類中不寫這兩個接口，只在ConcreteCompany 類中實現add remove等操作，但是這樣在使用這些類的時候, 由於樹葉和樹枝接口不同，就需要有一些判斷。