Python设计模式详解之11 —— 享元模式-优快云博客

本文链接：https://blog.youkuaiyun.com/huaanxiang/article/details/143946666

Flyweight（享元）设计模式是一种结构型设计模式，旨在通过共享相同的对象以减少内存使用和对象创建的开销。它非常适合应用于需要创建大量细粒度对象的场景，例如图形编辑器中的形状、文字处理软件中的字符等。

模式意图

目的：通过共享尽可能多的对象来支持大量细粒度对象的高效使用。
核心思想：将对象的状态分为内部状态和外部状态。
- 内部状态：对象共享的状态，存储在享元对象内部，不随环境改变。
- 外部状态：对象特有的状态，存储在客户端，由客户端传递给享元对象。

组成部分

以下是享元模式的核心结构：

+--------------------+        +--------------------+        +--------------------+        +--------------------+
|     Flyweight      |<-------| ConcreteFlyweight  |<-------|  FlyweightFactory  |<-------|      Client        |
+--------------------+        +--------------------+        +--------------------+        +--------------------+
| + operation(extr): |        | - intr: Any        |        | - flyweights: dict |        | - extr: Any        |
|   void             |        | + operation(extr): |        | + get_flyweight(   |        | + use_flyweight(): |
|                    |        |   void             |        |   key): Flyweight  |        |   void             |
+--------------------+        +--------------------+        | + create_flyweight(|        +--------------------+
                                                           |   key): Flyweight  |
                                                           +--------------------+

Flyweight（享元接口）
定义一个方法，用于接收外部状态。
ConcreteFlyweight（具体享元类）
实现享元接口，存储内部状态。
FlyweightFactory（享元工厂类）
管理享元对象的创建和共享，确保相同的享元对象被重复使用。
Client（客户端）
负责维护外部状态，并调用享元对象的方法。

Python实现

以下示例展示了使用享元模式优化绘制树的操作：

class TreeType:
    """享元类，表示树的类型（内部状态）"""
    def __init__(self, name, color, texture):
        self.name = name
        self.color = color
        self.texture = texture

    def draw(self, x, y):
        """绘制树时需要外部状态（位置）"""
        print(f"Drawing {self.name} tree at ({x}, {y}) with color {self.color} and texture {self.texture}")


class TreeFactory:
    """享元工厂类，管理树类型的共享"""
    _tree_types = {}

    @classmethod
    def get_tree_type(cls, name, color, texture):
        key = (name, color, texture)
        if key not in cls._tree_types:
            cls._tree_types[key] = TreeType(name, color, texture)
            print(f"Created new TreeType: {key}")
        else:
            print(f"Reusing existing TreeType: {key}")
        return cls._tree_types[key]


class Tree:
    """具体的树类，包含位置（外部状态）和树类型（享元）"""
    def __init__(self, x, y, tree_type):
        self.x = x
        self.y = y
        self.tree_type = tree_type

    def draw(self):
        self.tree_type.draw(self.x, self.y)


class Forest:
    """客户端类，管理树的集合"""
    def __init__(self):
        self.trees = []

    def plant_tree(self, x, y, name, color, texture):
        tree_type = TreeFactory.get_tree_type(name, color, texture)
        tree = Tree(x, y, tree_type)
        self.trees.append(tree)

    def draw(self):
        for tree in self.trees:
            tree.draw()


# 使用示例
forest = Forest()
forest.plant_tree(10, 20, "Oak", "Green", "Rough")
forest.plant_tree(15, 25, "Oak", "Green", "Rough")
forest.plant_tree(20, 30, "Pine", "Dark Green", "Smooth")
forest.draw()

输出示例

Created new TreeType: ('Oak', 'Green', 'Rough')
Reusing existing TreeType: ('Oak', 'Green', 'Rough')
Created new TreeType: ('Pine', 'Dark Green', 'Smooth')
Drawing Oak tree at (10, 20) with color Green and texture Rough
Drawing Oak tree at (15, 25) with color Green and texture Rough
Drawing Pine tree at (20, 30) with color Dark Green and texture Smooth