工厂方法模式

工厂方法模式

代码实例参考于《HeadFirst设计模式》。
工厂（factory）处理创建对象的细节。

抽象类

public abstract class Pizza {
    String name;
    String dough;
    String sauce;
    ArrayList toppings = new ArrayList();

    void prepare() {
        System.out.println("Preparing " + name);
        System.out.println("Tossing dough... ");
        System.out.println("Adding sauce... ");
        System.out.println("Adding toppings:");
        for (int i = 0; i < toppings.size(); i++) {
            System.out.println("  " + toppings.get(i));
        }
    }

    void bake() {
        System.out.println("Bake for 25 minutes at 350");
    }

    void cut() {
        System.out.println("Cutting the pizza into diagonal slices");
    }

    void box() {
        System.out.println("Place pizza in official PizzaStore box");
    }

    public String getName() {
        return name;
    }
}

声明工厂方法

public abstract class PizzaStore {
    public Pizza orderPizza(String type) {
        Pizza pizza;
        pizza = createPizza(type);
        pizza.prepare();
        pizza.bake();
        pizza.cut();
        pizza.box();
        return pizza;
    }
    // 创建pizza对象
    protected abstract Pizza createPizza(String type);
}

工厂的具体实现

// 纽约披萨工厂
public class NYPizzaStore extends PizzaStore {
    @Override
    protected Pizza createPizza(String type) {
        if (type.equals("cheese")) {
            return new NYStyleCheesePizza();
        } else {
            return null;
        }
    }
}
// 芝加哥披萨工厂
public class ChicagoPizzaStore extends PizzaStore {
    @Override
    protected Pizza createPizza(String type) {
        if (type.equals("cheese")) {
            return new ChicagoStyleCheesePizza();
        } else {
            return null;
        }
    }
}

具体的Pizza

// 纽约风味的芝士披萨
public class NYStyleCheesePizza extends Pizza {
    public NYStyleCheesePizza() {
        name = "NY Style Sauce and Cheese Pizza";
        dough = "Thin Crust Dough";
        sauce = "Marinara Sauce";

        toppings.add("Grated Reggiano Cheese");
    }
}
// 芝加哥风味的芝士披萨
public class ChicagoStyleCheesePizza extends Pizza {
    public ChicagoStyleCheesePizza() {
        name = "Chicago Style Deep Dish Cheese Pizza";
        dough = "Extra Thick Crust Dough";
        sauce = "Plum Tomato Sauce";

        toppings.add("Shredded Mozzarella Cheese");
    }

    @Override
    void cut() {
        System.out.println("Cutting the pizza into square slices");
    }
}

测试类

public class PizzaTestDrive {
    public static void main(String[] args) {
        PizzaStore nyStore = new NYPizzaStore();
        PizzaStore chicagoStore = new ChicagoPizzaStore();

        Pizza pizza = nyStore.orderPizza("cheese");
        System.out.println("Ethan ordered a " + pizza.getName() + "\n");

        pizza = chicagoStore.orderPizza("cheese");
        System.out.println("Ethan ordered a " + pizza.getName() + "\n");
    }
}