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在 Head First Design Pattern 一书中，我不明白为什么 PizzaTestDrive 类会创建 SimplePizzaFactory 类的对象。为什么 PizzaStore 类不创建您自己的对象？

public class PizzaTestDrive {

    public static void main(String[] args) {
        SimplePizzaFactory factory = new SimplePizzaFactory();
        PizzaStore store = new PizzaStore(factory);

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

        pizza = store.orderPizza("veggie");
        System.out.println("We ordered a " + pizza.getName() + "\n");
    }
}

public class PizzaStore {
    SimplePizzaFactory factory;

    public PizzaStore(SimplePizzaFactory factory) { 
        this.factory = factory;
    }

    public Pizza orderPizza(String type) {
        Pizza pizza;

        pizza = factory.createPizza(type);

        pizza.prepare();
        pizza.bake();
        pizza.cut();
        pizza.box();

        return pizza;
    }

}

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

    public String getName() {
        return name;
    }

    public void prepare() {
        System.out.println("Preparing " + name);
    }

    public void bake() {
        System.out.println("Baking " + name);
    }

    public void cut() {
        System.out.println("Cutting " + name);
    }

    public void box() {
        System.out.println("Boxing " + name);
    }

    public String toString() {
        // code to display pizza name and ingredients
        StringBuffer display = new StringBuffer();
        display.append("---- " + name + " ----\n");
        display.append(dough + "\n");
        display.append(sauce + "\n");
        for (int i = 0; i < toppings.size(); i++) {
            display.append((String )toppings.get(i) + "\n");
        }
        return display.toString();
    }
}

public class SimplePizzaFactory {

    public Pizza createPizza(String type) {
        Pizza pizza = null;

        if (type.equals("cheese")) {
            pizza = new CheesePizza();
        } else if (type.equals("pepperoni")) {
            pizza = new PepperoniPizza();
        } else if (type.equals("clam")) {
            pizza = new ClamPizza();
        } else if (type.equals("veggie")) {
            pizza = new VeggiePizza();
        }
        return pizza;
    }
}

public class CheesePizza extends Pizza {
    public CheesePizza() {
        name = "Cheese Pizza";
        dough = "Regular Crust";
        sauce = "Marinara Pizza Sauce";
        toppings.add("Fresh Mozzarella");
        toppings.add("Parmesan");
    }
}

public class ClamPizza extends Pizza {
    public ClamPizza() {
        name = "Clam Pizza";
        dough = "Thin crust";
        sauce = "White garlic sauce";
        toppings.add("Clams");
        toppings.add("Grated parmesan cheese");
    }
}


public class PepperoniPizza extends Pizza {
    public PepperoniPizza() {
        name = "Pepperoni Pizza";
        dough = "Crust";
        sauce = "Marinara sauce";
        toppings.add("Sliced Pepperoni");
        toppings.add("Sliced Onion");
        toppings.add("Grated parmesan cheese");
    }
}


public class VeggiePizza extends Pizza {
    public VeggiePizza() {
        name = "Veggie Pizza";
        dough = "Crust";
        sauce = "Marinara sauce";
        toppings.add("Shredded mozzarella");
        toppings.add("Grated parmesan");
        toppings.add("Diced onion");
        toppings.add("Sliced mushrooms");
        toppings.add("Sliced red pepper");
        toppings.add("Sliced black olives");
    }
}

比萨班准备比萨。SimplePizzaFactory 选择要制作的披萨。PizzaStore 将比萨“卖”给客户。PizzaTestDrive 是客户。

4

1 回答 1

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Because the author chose to design it that way.

You might see it as a Pizza store getting frozen pizzas from a factory, and then preparing, baking, cutting and boxing them.

The design separates the responsibility of creating a pizza from a name (that's what the PizzaFactory does), and of selling them cooked and boxed to customers (that's what the PizzaStore does).

The PizzaStore could choose to use another fozen pizza vendor, which would create pizzas differently. But the preparation, baking and boxing of the pizza store would still work the same way.

于 2013-10-30T12:16:04.813 回答