结构型 | 享元模式

Flyweight Pattern (享元模式)，主要用于减少创建对象的数量，以减少内存占用和提高性能。

题图#

通过共享多个对象所共有的相同状态，让有限的内存容量中载入更多对象。

场景#

数量巨大的相似对象
设备内存有限
对象中包含可抽取且能在多个对象间共享的重复状态

应用：

数据库连接池

缺点#

系统复杂度提高
读取外外部状态运行时间变长

实现#

//  1. 创建一个接口
interface Shape {
  draw(): void;
}

//  2. 创建实现接口的实体类
class Circle implements Shape {
  private color: string;
  private x: number = 0;
  private y: number = 0;
  private radius: number = 0;

  constructor(color: string) {
    this.color = color;
  }

  public setX(x: number): void {
    this.x = x;
  }

  public setY(y: number): void {
    this.y = y;
  }

  public setRadius(radius: number): void {
    this.radius = radius;
  }

  public draw(): void {
    console.log(
      "Circle: Draw() [Color : " +
        this.color +
        ", x : " +
        this.x +
        ", y :" +
        this.y +
        ", radius :" +
        this.radius
    );
  }
}

// 3. 创建一个工厂，生成基于给定信息的实体类的对象
class ShapeFactory {
  private static circleMap = new Map<string, Shape>();

  public static getCircle(color: string): Shape {
    let circle: Circle = <Circle>this.circleMap.get(color);

    if (circle == null) {
      circle = new Circle(color);
      this.circleMap.set(color, circle);
      console.log("Creating circle of color : " + color);
    }
    return circle;
  }
}

测试

//  4. 使用该工厂，通过传递颜色信息来获取实体类的对象
class FlyweightPatternDemo {
  private static colors: string[] = ["Red", "Green", "Blue", "White", "Black"];
  constructor() {
    for (let i: number = 0; i < 20; ++i) {
      let circle: Circle = <Circle>(
        ShapeFactory.getCircle(FlyweightPatternDemo.getRandomColor())
      );
      circle.setX(FlyweightPatternDemo.getRandomX());
      circle.setY(FlyweightPatternDemo.getRandomY());
      circle.setRadius(100);
      circle.draw();
    }
  }

  private static getRandomColor(): string {
    return this.colors[Math.floor(Math.random() * this.colors.length)];
  }

  private static getRandomX(): number {
    return Math.floor(Math.random() * 100);
  }

  private static getRandomY(): number {
    return Math.floor(Math.random() * 100);
  }
}
//  test
new FlyweightPatternDemo();

// Creating circle of color : Green
// Circle: Draw() [Color : Green, x : 37, y :72, radius :100
// Creating circle of color : Blue
// Circle: Draw() [Color : Blue, x : 9, y :87, radius :100
// Creating circle of color : White
// Circle: Draw() [Color : White, x : 24, y :77, radius :100
// Circle: Draw() [Color : Green, x : 56, y :71, radius :100
// Circle: Draw() [Color : White, x : 84, y :92, radius :100
// Circle: Draw() [Color : Green, x : 37, y :36, radius :100
// Creating circle of color : Black
// Circle: Draw() [Color : Black, x : 85, y :1, radius :100
// Creating circle of color : Red
// Circle: Draw() [Color : Red, x : 74, y :57, radius :100
// Circle: Draw() [Color : Green, x : 75, y :91, radius :100
// Circle: Draw() [Color : Blue, x : 85, y :9, radius :100
// Circle: Draw() [Color : Blue, x : 94, y :17, radius :100
// Circle: Draw() [Color : Black, x : 32, y :64, radius :100
// Circle: Draw() [Color : White, x : 89, y :26, radius :100
// Circle: Draw() [Color : Green, x : 63, y :90, radius :100
// Circle: Draw() [Color : Red, x : 20, y :15, radius :100
// Circle: Draw() [Color : Red, x : 54, y :57, radius :100
// Circle: Draw() [Color : White, x : 26, y :94, radius :100
// Circle: Draw() [Color : Green, x : 99, y :64, radius :100
// Circle: Draw() [Color : Green, x : 64, y :29, radius :100
// Circle: Draw() [Color : Black, x : 20, y :46, radius :100