一. 定义

         工厂方法模式定义了一个创建对象的接口，但由子类决定要实例化的类是哪一个。工厂方法让类把实例化推迟到子类。

二. 模式起源

三. 设计原则

四. UML图

五. 代码

5.1 水果父类

package model.factory;

/**
 * 水果父类
 */
public abstract class Fruit {

    /**
     * 展示是哪种水果
     */
    public abstract void show();

}

5.2 A工厂生产的苹果类

package model.factory;

/**
 * A工厂生产的苹果类
 */
public class AApple extends Fruit {

    @Override
    public void show() {
        System.out.println("I am an apple made in AFruitFactory");
    }
}

5.3 A工厂生产的香蕉类

package model.factory;

/**
 *  A工厂生产的香蕉类
 */
public class ABanana extends Fruit {

    @Override
    public void show() {
        System.out.println("I am a banana made in AFruitFactory");
    }
}

5.4 A工厂生产的橘子类

package model.factory;

/**
 * A工厂生产的橘子类
 */
public class AOrange extends Fruit {

    @Override
    public void show() {
        System.out.println("I am an orange made in AFruitFactory");
    }
}

5.5 B工厂生产的苹果类

package model.factory;

/**
 * B工厂生产的苹果类
 */
public class BApple extends Fruit {

    @Override
    public void show() {
        System.out.println("I am an apple made in BFruitFactory");
    }
}

5.6 B工厂生产的香蕉类

package model.factory;

/**
 * B工厂生产的香蕉类
 */
public class BBanana extends Fruit {

    @Override
    public void show() {
        System.out.println("I am a banana made in BFruitFactory");
    }
}

5.7 B工厂生产的橘子类

package model.factory;

/**
 * B工厂生产的橘子类
 */
public class BOrange extends Fruit {

    @Override
    public void show() {
        System.out.println("I am an orange made in BFruitFactory");
    }
}

5.8 水果商店类

package model.factory;

/**
 * 水果商店类
 */
public abstract class FruitStore {

    /**
     * 订购水果
     * @param type 水果类型
     * @return 水果
     */
    public Fruit orderFruit(String type) {

        // 此处交由子类作为工厂来生产水果，this: 只要父类为FruitStore的子类都可以
        Fruit fruit = this.createFruit(type);

        return fruit;
    }

    /**
     * 生产水果
     * @param type 水果类型
     * @return 水果
     */
    protected  abstract Fruit createFruit(String type);
}

5.9 A水果工厂类

package model.factory;

/**
 * A水果工厂类
 */
public class AFruitFactory extends FruitStore {

    @Override
    protected Fruit createFruit(String type) {

        Fruit fruit = null;

        if (type.equals("apple")) {
            fruit = new AApple();
        } else if (type.equals("banana")) {
            fruit = new ABanana();
        } else if (type.equals("orange")) {
            fruit = new AOrange();
        }

        return fruit;
    }
}

5.10 B水果工厂类

package model.factory;

/**
 * B水果工厂类
 */
public class BFruitFactory extends FruitStore {

    @Override
    protected Fruit createFruit(String type) {

        Fruit fruit = null;

        if (type.equals("apple")) {
            fruit = new BApple();
        } else if (type.equals("banana")) {
            fruit = new BBanana();
        } else if (type.equals("orange")) {
            fruit = new BOrange();
        }

        return fruit;
    }
}

5.11 测试

package model.factory;

public class Main {

    public static void main(String[] args) {

        FruitStore aFruitFactory = new AFruitFactory();
        FruitStore bFruitFactory = new BFruitFactory();

        Fruit fruit = aFruitFactory.createFruit("apple");
        fruit.show();

        fruit = bFruitFactory.createFruit("apple");
        fruit.show();
    }

}

5.12 结果

I am an apple made in AFruitFactory
I am an apple made in BFruitFactory

六. 感悟

      皮一下：  Head First设计模式中文版 P122页  印刷错误 ： 但由于Pizza对象是抽象的，  中应该为PizzaStore而非Pizza.   截图如下：