工厂模式

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。

示例—披萨店

一家披萨店，有很多种口味的披萨可接收下单。为了扩展加盟店，每个披萨从制作到最后出炉，都有一套统一标准化的流程。流程包括准备所有的披萨的配料、准备制作（加酱料、揉面团等）、烘烤、切角、装盒。披萨本身有自己的名称、需要的生面团、酱料以及其他配料。现有纽约和芝加哥两个加盟店，虽然他们店中的披萨种类都一样，但实际出来的口味是不同的，比如纽约芝士披萨（大蒜蕃茄酱以及薄饼）和芝加哥芝士披萨（小蕃茄酱以及厚饼）。所有加盟店的流程以及披萨的种类都是一致的。

UML图表示

工厂模式-披萨店

代码演示

披萨抽象基类

package Factory;

import java.util.ArrayList;

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");
    }

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

    public String getName() {
        return name;
    }
}

纽约披萨子类

package Factory;

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");
    }
}

芝加哥披萨子类

package Factory;

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");
    }
}

披萨店抽象基类

package Factory;

public abstract class PizzaStore {
    public Pizza orderPizza(String type) {
        Pizza pizza;
        pizza = createPizza(type);

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

        return pizza;

    }

    protected abstract Pizza createPizza(String type);
}

纽约披萨店子类

package Factory;

public class NYPizzaStore extends PizzaStore {
    @Override
    protected Pizza createPizza(String type) {
        if (type.equals("cheese")) {
            return new NYStyleCheesePizza();
        }
        else if (type.equals("veggie")){
            // return new NYStyleVeggiePizza();
        }
        else if (type.equals("clam")){
            // return new NYStyleClamPizza();
        }
        else if (type.equals("pepperoni")){
            // return new NYStylePepperoniPizza();
        }

        return null;
    }
}

芝加哥披萨店子类

package Factory;

public class ChicagoPizzaStore extends PizzaStore {

    @Override
    protected Pizza createPizza(String type) {
        if (type.equals("cheese")) {
            return new ChicagoStyleCheesePizza();
        }
        else if (type.equals("veggie")){
            // return new ChicagoStyleVeggiePizza();
        }
        else if (type.equals("clam")){
            // return new ChicagoStyleClamPizza();
        }
        else if (type.equals("pepperoni")){
            // return new ChicagoStylePepperoniPizza();
        }

        return null;
    }
}

披萨下单测试代码

package Factory;

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("Joel ordered a " + pizza.getName() + "\n");
    }
}

测试结果

Preparing NY Style Sauce and Cheese Pizza
Tossing dough...
Adding sauce...
Adding toppings: 
  Grated Reggiano Cheese
Bake for 25 minutes at 350
Cutting the pizza into diagonal
Place pizza in official PizzaStore box
Ethan ordered a NY Style Sauce and Cheese Pizza

Preparing Chicago Style Deep Dish Cheese Pizza
Tossing dough...
Adding sauce...
Adding toppings: 
  Shredded Mozzarella Cheese
Bake for 25 minutes at 350
Cutting the pizza into square slices
Place pizza in official PizzaStore box
Joel ordered a Chicago Style Deep Dish Cheese Pizza