Day 06: Creational patterns - Factory Method

目的

不再限制一个工厂（物件）建立许多产品（物件），而是转变成一个产品（物件）对应一个工厂（物件），而决定生产哪个产品（物件）则转交给另一个决策者（物件）。

说明

昨天提到，每次新增一个产品时，Simple Factory Method 内负责管理生产的工厂就必须「变动 switch-case」，此项举动违反 SOLID 的 OCP。Factory Method 改良这一点，让每项产品拥有各自的工厂。实际决定要使用哪间工厂的决策者，则转交给其他物件负责，本身不涉入生产判定。

Factory Method 的作法是：

先决定要建立的产品，该产品视为亲代，可以用 Class、Abstract Class 或 Interface。
建立一系列的产品子代，子代负责实作细节。
建立工厂的亲代，使用 Interface。
建立一系列的的工厂子代，工厂与产品的关系是一对一，一个产品只有一间工厂，负责实作细节。
决策者决定使用哪间工厂得到想要的产品。

UML 图

Factory Method UML Diagram

使用 Java 实作

产品亲代：PETBottle

public abstract class PETBottle {
    protected String smell = "";
    protected String color = "";

    public PETBottle(String smell, String color) {
        this.smell = smell;
        this.color = color;
    }

    public abstract String getTaste();
}

产品子代：Coke、Water、OrangeJuice

public class Coke extends PETBottle {
    public Coke(String smell, String color) {
        super(smell, color);
    }

    @Override
    public String getTaste() {
        return "这瓶可乐的颜色：" + color + "，香味是：" + smell;
    }
}

public class Water extends PETBottle {
    public Water(String smell, String color) {
        super(smell, color);
    }

    @Override
    public String getTaste() {
        return "这瓶水的颜色：" + color + "，香味是：" + smell;
    }
}

public class OrangeJuice extends PETBottle {
    public OrangeJuice(String smell, String color) {
        super(smell, color);
    }

    @Override
    public String getTaste() {
        return "这瓶柳橙汁的颜色：" + color + "，香味是：" + smell;
    }
}

工厂亲代：PETBottleFactory

public interface PETBottleFactory {
    public PETBottle getPET_Bottle();
}

工厂子代：CokeFactory、WaterFactory、OrangeJuiceFactory

public class CokeFactory implements PETBottleFactory {
    @Override
    public PETBottle getPET_Bottle() {
        System.out.println("机器选定可乐瓶子");
        System.out.println("黑色液体冲入瓶子内");
        System.out.println("转上瓶盖，完成");
        return new Coke("甜甜的", "黑色");
    }
}

public class OrangeJuiceFactory implements PETBottleFactory {
    @Override
    public PETBottle getPET_Bottle() {
        System.out.println("机器选定矿泉柳橙汁瓶子");
        System.out.println("橘色液体冲入瓶子内");
        System.out.println("转上瓶盖，完成");
        return new OrangeJuice("酸酸的", "橘色");
    }
}

public class WaterFactory implements PETBottleFactory {
    @Override
    public PETBottle getPET_Bottle() {
        System.out.println("机器选定矿泉水瓶子");
        System.out.println("透明液体冲入瓶子内");
        System.out.println("转上瓶盖，完成");
        return new Water("无味", "透明的");
    }
}

决策者：

public class PETBottleFactoryMethodSample {
    public static void main(String[] args) {
        System.out.println("今天我想来点，可乐！");
        PETBottleFactory cokeFactory = new CokeFactory();
        PETBottle coke = cokeFactory.getPET_Bottle();
        System.out.println("得到一瓶可乐！");
        System.out.println(coke.getTaste());
        System.out.println("---咳咳咳---");

        System.out.println("有点甜，我想喝点，矿泉水！");
        PETBottleFactory waterFactory = new WaterFactory();
        PETBottle water = waterFactory.getPET_Bottle();
        System.out.println("得到一瓶矿泉水！");
        System.out.println(water.getTaste());

        System.out.println("---咕噜咕噜---");

        System.out.println("清爽！最来来点，柳橙汁！");
        PETBottleFactory orangeJuiceFactory = new OrangeJuiceFactory();
        PETBottle orangeJuice = orangeJuiceFactory.getPET_Bottle();
        System.out.println("得到一瓶柳橙汁！");
        System.out.println(orangeJuice.getTaste());
    }
}

使用 JavaScript 实作

受限於 JavaScript 没有虚拟型别、无法限制型别。

产品亲代：PETBottle

/** @abstract */
class PETBottle {
  constructor(smell, color) {
    this.smell = smell;
    this.color = color;
  }

  getTaste() { return; }
}

产品子代：Coke、Water、OrangeJuice

class Coke extends PETBottle {
  constructor(smell, color) {
    super(smell, color);
  }

  /** @override */
  getTaste() {
    return "这瓶可乐的颜色：" + this.color + "，香味是：" + this.smell;
  }
}

class Water extends PETBottle {
  constructor(smell, color) {
    super(smell, color);
  }

  /** @override */
  getTaste() {
    return "这瓶水的颜色：" + this.color + "，香味是：" + this.smell;
  }
}

class OrangeJuice extends PETBottle {
  constructor(smell, color) {
    super(smell, color);
  }

  /** @override */
  getTaste() {
    return "这瓶柳橙汁的颜色：" + this.color + "，香味是：" + this.smell;
  }
}

工厂亲代：PETBottleFactory

/** @interface */
class PETBottleFactory {
  getPET_Bottle() { return; }
}

工厂子代：CokeFactory、WaterFactory、OrangeJuiceFactory

class CokeFactory extends PETBottleFactory {
  /** @override */
  getPET_Bottle() {
    console.log("机器选定可乐瓶子");
    console.log("黑色液体冲入瓶子内");
    console.log("转上瓶盖，完成");
    return new Coke("甜甜的", "黑色");
  }
}

class WaterFactory extends PETBottleFactory {
  /** @override */
  getPET_Bottle() {
    console.log("机器选定矿泉水瓶子");
    console.log("透明液体冲入瓶子内");
    console.log("转上瓶盖，完成");
    return new Coke("甜甜的", "黑色");
  }
}

class OrangeJuiceFactory extends PETBottleFactory {
  /** @override */
  getPET_Bottle() {
    console.log("机器选定矿泉柳橙汁瓶子");
    console.log("橘色液体冲入瓶子内");
    console.log("转上瓶盖，完成");
    return new OrangeJuice("酸酸的", "橘色");
  }
}

决策者：

const PETBottleFactoryMethodSample = () => {
  console.log("今天我想来点，可乐！");
  const cokeFactory = new CokeFactory();
  const coke = cokeFactory.getPET_Bottle();
  console.log("得到一瓶可乐！");
  console.log(coke.getTaste());
  console.log("---咳咳咳---");

  console.log("有点甜，我想喝点，矿泉水！");
  const waterFactory = new WaterFactory();
  const water = waterFactory.getPET_Bottle();
  console.log("得到一瓶矿泉水！");
  console.log(water.getTaste());

  console.log("---咕噜咕噜---");

  console.log("清爽！最来来点，柳橙汁！");
  const orangeJuiceFactory = new OrangeJuiceFactory();
  const orangeJuice = orangeJuiceFactory.getPET_Bottle();
  console.log("得到一瓶柳橙汁！");
  console.log(orangeJuice.getTaste());
};

PETBottleFactoryMethodSample();