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工厂方法

工厂方法在 Python 中的实现

工厂方法是一种创建型设计模式 解决了在不指定具体类的情况下创建产品对象的问题

工厂方法定义了一个方法 且必须使用该方法代替通过直接调用构造函数来创建对象 new 操作符 的方式 子类可重写该方法来更改将被创建的对象所属类

如果你不清楚工厂 工厂方法抽象工厂模式之间的区别 请参阅工厂模式比较

在 Python 中使用模式

复杂度

流行度

使用示例 工厂方法模式在 Python 代码中得到了广泛使用 当你需要在代码中提供高层次的灵活性时 该模式会非常实用

识别方法 工厂方法可通过构建方法来识别 它会创建具体类的对象 但以抽象类型或接口的形式返回这些对象

概念示例

本例说明了工厂方法设计模式的结构并重点回答了下面的问题

  • 它由哪些类组成
  • 这些类扮演了哪些角色
  • 模式中的各个元素会以何种方式相互关联

main.py: 概念示例

from __future__ import annotations
from abc import ABC, abstractmethod


class Creator(ABC):
    """
    The Creator class declares the factory method that is supposed to return an
    object of a Product class. The Creator's subclasses usually provide the
    implementation of this method.
    """

    @abstractmethod
    def factory_method(self):
        """
        Note that the Creator may also provide some default implementation of
        the factory method.
        """
        pass

    def some_operation(self) -> str:
        """
        Also note that, despite its name, the Creator's primary responsibility
        is not creating products. Usually, it contains some core business logic
        that relies on Product objects, returned by the factory method.
        Subclasses can indirectly change that business logic by overriding the
        factory method and returning a different type of product from it.
        """

        # Call the factory method to create a Product object.
        product = self.factory_method()

        # Now, use the product.
        result = f"Creator: The same creator's code has just worked with {product.operation()}"

        return result


"""
Concrete Creators override the factory method in order to change the resulting
product's type.
"""


class ConcreteCreator1(Creator):
    """
    Note that the signature of the method still uses the abstract product type,
    even though the concrete product is actually returned from the method. This
    way the Creator can stay independent of concrete product classes.
    """

    def factory_method(self) -> ConcreteProduct1:
        return ConcreteProduct1()


class ConcreteCreator2(Creator):
    def factory_method(self) -> ConcreteProduct2:
        return ConcreteProduct2()


class Product(ABC):
    """
    The Product interface declares the operations that all concrete products
    must implement.
    """

    @abstractmethod
    def operation(self) -> str:
        pass


"""
Concrete Products provide various implementations of the Product interface.
"""


class ConcreteProduct1(Product):
    def operation(self) -> str:
        return "{Result of the ConcreteProduct1}"


class ConcreteProduct2(Product):
    def operation(self) -> str:
        return "{Result of the ConcreteProduct2}"


def client_code(creator: Creator) -> None:
    """
    The client code works with an instance of a concrete creator, albeit through
    its base interface. As long as the client keeps working with the creator via
    the base interface, you can pass it any creator's subclass.
    """

    print(f"Client: I'm not aware of the creator's class, but it still works.\n"
          f"{creator.some_operation()}", end="")


if __name__ == "__main__":
    print("App: Launched with the ConcreteCreator1.")
    client_code(ConcreteCreator1())
    print("\n")

    print("App: Launched with the ConcreteCreator2.")
    client_code(ConcreteCreator2())

Output.txt: 执行结果

App: Launched with the ConcreteCreator1.
Client: I'm not aware of the creator's class, but it still works.
Creator: The same creator's code has just worked with {Result of the ConcreteProduct1}

App: Launched with the ConcreteCreator2.
Client: I'm not aware of the creator's class, but it still works.
Creator: The same creator's code has just worked with {Result of the ConcreteProduct2}

工厂方法在其他编程语言中的实现

工厂方法在 C# 中的实现 工厂方法在 Java 中的实现 工厂方法在 PHP 中的实现 工厂方法在 Ruby 中的实现 工厂方法在 Swift 中的实现 工厂方法在 TypeScript 中的实现