1.介紹

它是定義一個創建對象的接口，但由子類決定要實例化的類是哪一個，工廠方法讓類把實例化推遲到子類中。

2.小栗子

Pizza店做Pizza

3.代碼實現

// Pizza抽象類
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.");
    }
}

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

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

// 西雅圖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();
    }
    
    // 工廠方法模式
    protected abstract Pizza createPizza(PizzaIngredientFactory factory);
}

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

4.測試

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.總結

紐約可以做紐約/西雅圖等地區風格的Pizza，而且Pizza本身風格也是可以擴展的。

源碼地址：https://gitee.com/jsjack_wang/JavaDemo