1.介绍

它是定义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中。

2.小栗子

Pizza店做Pizza

3.代码实现

// Pizza抽象类
public abstract class Pizza {
    protected PizzaIngredientFactory factory = null;

    public Pizza(PizzaIngredientFactory factory) {
        this.factory = factory;
    }

    public abstract String getName();

    public void prepare() {
        System.out.println("Dough:" + factory.createDough().getName());
        System.out.println("Sauce:" + factory.createSauce().getName());
        System.out.println(this.getName() + " prepare success.");
    }
}

// 纽约Pizza
public class NYPizza extends Pizza {
    public NYPizza(PizzaIngredientFactory factory) {
        super(factory);
    }

    @Override
    public String getName() {
        return "NY Pizza";
    }
}

// 西雅图Pizza
public class SeattlePizza extends Pizza {
    public SeattlePizza(PizzaIngredientFactory factory) {
        super(factory);
    }

    @Override
    public String getName() {
        return "Seattle Pizza";
    }
}

// Pizza店 做Pizza
public abstract class PizzaStore {
    public void orderPizza(PizzaIngredientFactory factory) {
        Pizza pizza = createPizza(factory);
        pizza.prepare();
    }
    
    // 工厂方法模式
    protected abstract Pizza createPizza(PizzaIngredientFactory factory);
}

// 纽约PizzaStore
public class NYPizzaStore extends PizzaStore {
    @Override
    protected Pizza createPizza(PizzaIngredientFactory factory) {
        return new NYPizza(factory);
    }
}

4.测试

public class FactoryMethodPatternDemo {
    public static void main(String[] args) {
        PizzaIngredientFactory nyFactory = new NYPizzaIngredientFactory();
        PizzaIngredientFactory seattleFactory = new SeattlePizzaIngredientFactory();

        PizzaStore pizzaStore = new NYPizzaStore();
        pizzaStore.orderPizza(seattleFactory);

        pizzaStore.orderPizza(nyFactory);
    }
}

5.总结

纽约可以做纽约/西雅图等地区风格的Pizza，而且Pizza本身风格也是可以扩展的。

源码地址：https://gitee.com/jsjack_wang/JavaDemo