设计模式――工厂方法模式（Factory Method Pattern）

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。

类图

（图片源于网络）

代码实现（Java）

产品类

// Pizza.java
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;
    }
    public String toString() {
        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();
    }
}

// NYStyleCheesePizza.java
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");
    }
}

// NYStylePepperoniPizza.java
public class NYStylePepperoniPizza extends Pizza {
    public NYStylePepperoniPizza() {
        name = "NY Style Pepperoni Pizza";
        dough = "Thin Crust Dough";
        sauce = "Marinara Sauce";
                                                                     
        toppings.add("Grated Reggiano Cheese");
        toppings.add("Sliced Pepperoni");
        toppings.add("Garlic");
        toppings.add("Onion");
        toppings.add("Mushrooms");
        toppings.add("Red Pepper");
    }
}

// NYStyleClamPizza.java
public class NYStyleClamPizza extends Pizza {
    public NYStyleClamPizza() {
        name = "NY Style Clam Pizza";
        dough = "Thin Crust Dough";
        sauce = "Marinara Sauce";
                                                             
        toppings.add("Grated Reggiano Cheese");
        toppings.add("Fresh Clams from Long Island Sound");
    }
}

// NYStyleVeggiePizza.java
public class NYStyleVeggiePizza extends Pizza {
    public NYStyleVeggiePizza() {
        name = "NY Style Veggie Pizza";
        dough = "Thin Crust Dough";
        sauce = "Marinara Sauce";
                                                         
        toppings.add("Grated Reggiano Cheese");
        toppings.add("Garlic");
        toppings.add("Onion");
        toppings.add("Mushrooms");
        toppings.add("Red Pepper");
    }
}

// ChicagoStyleCheesePizza.java
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");
    }
    void cut() {
        System.out.println("Cutting the pizza into square slices");
    }
}

// ChicagoStylePepperoniPizza.java
public class ChicagoStylePepperoniPizza extends Pizza {
    public ChicagoStylePepperoniPizza() {
        name = "Chicago Style Pepperoni Pizza";
        dough = "Extra Thick Crust Dough";
        sauce = "Plum Tomato Sauce";
        toppings.add("Shredded Mozzarella Cheese");
        toppings.add("Black Olives");
        toppings.add("Spinach");
        toppings.add("Eggplant");
        toppings.add("Sliced Pepperoni");
    }
    void cut() {
        System.out.println("Cutting the pizza into square slices");
    }
}

// ChicagoStyleClamPizza.java
public class ChicagoStyleClamPizza extends Pizza {
    public ChicagoStyleClamPizza() {
        name = "Chicago Style Clam Pizza";
        dough = "Extra Thick Crust Dough";
        sauce = "Plum Tomato Sauce";
        toppings.add("Shredded Mozzarella Cheese");
        toppings.add("Frozen Clams from Chesapeake Bay");
    }
    void cut() {
        System.out.println("Cutting the pizza into square slices");
    }
}

// ChicagoStyleVeggiePizza.java
public class ChicagoStyleVeggiePizza extends Pizza {
    public ChicagoStyleVeggiePizza() {
        name = "Chicago Deep Dish Veggie Pizza";
        dough = "Extra Thick Crust Dough";
        sauce = "Plum Tomato Sauce";
        toppings.add("Shredded Mozzarella Cheese");
        toppings.add("Black Olives");
        toppings.add("Spinach");
        toppings.add("Eggplant");
    }
    void cut() {
        System.out.println("Cutting the pizza into square slices");
    }
}

创造者类

// PizzaStore.java
public abstract class PizzaStore {
                          
    abstract Pizza createPizza(String item);
                          
    public Pizza orderPizza(String type) {
        Pizza pizza = createPizza(type);
        System.out.println("--- Making a " + pizza.getName() + " ---");
        pizza.prepare();
        pizza.bake();
        pizza.cut();
        pizza.box();
        return pizza;
    }
}

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

// ChicagoPizzaStore.java
public class ChicagoPizzaStore extends PizzaStore {
    Pizza createPizza(String item) {
            if (item.equals("cheese")) {
                    return new ChicagoStyleCheesePizza();
            } else if (item.equals("veggie")) {
                    return new ChicagoStyleVeggiePizza();
            } else if (item.equals("clam")) {
                    return new ChicagoStyleClamPizza();
            } else if (item.equals("pepperoni")) {
                    return new ChicagoStylePepperoniPizza();
            } else return null;
    }
}

测试代码

// PizzaTestDrive.java
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");
        pizza = nyStore.orderPizza("clam");
        System.out.println("Ethan ordered a " + pizza.getName() + "\n");
               
        pizza = chicagoStore.orderPizza("clam");
        System.out.println("Joel ordered a " + pizza.getName() + "\n");
        pizza = nyStore.orderPizza("pepperoni");
        System.out.println("Ethan ordered a " + pizza.getName() + "\n");
               
        pizza = chicagoStore.orderPizza("pepperoni");
        System.out.println("Joel ordered a " + pizza.getName() + "\n");
        pizza = nyStore.orderPizza("veggie");
        System.out.println("Ethan ordered a " + pizza.getName() + "\n");
               
        pizza = chicagoStore.orderPizza("veggie");
        System.out.println("Joel ordered a " + pizza.getName() + "\n");
    }
}

运行效果

--- Making a NY Style Sauce and Cheese Pizza --- 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 slices Place pizza in official PizzaStore box Ethan ordered a NY Style Sauce and Cheese Pizza --- Making a Chicago Style Deep Dish 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 --- Making a NY Style Clam Pizza --- Preparing NY Style Clam Pizza Tossing dough... Adding sauce... Adding toppings: Grated Reggiano Cheese Fresh Clams from Long Island Sound Bake for 25 minutes at 350 Cutting the pizza into diagonal slices Place pizza in official PizzaStore box Ethan ordered a NY Style Clam Pizza --- Making a Chicago Style Clam Pizza --- Preparing Chicago Style Clam Pizza Tossing dough... Adding sauce... Adding toppings: Shredded Mozzarella Cheese Frozen Clams from Chesapeake Bay Bake for 25 minutes at 350 Cutting the pizza into square slices Place pizza in official PizzaStore box Joel ordered a Chicago Style Clam Pizza --- Making a NY Style Pepperoni Pizza --- Preparing NY Style Pepperoni Pizza Tossing dough... Adding sauce... Adding toppings: Grated Reggiano Cheese Sliced Pepperoni Garlic Onion Mushrooms Red Pepper Bake for 25 minutes at 350 Cutting the pizza into diagonal slices Place pizza in official PizzaStore box Ethan ordered a NY Style Pepperoni Pizza --- Making a Chicago Style Pepperoni Pizza --- Preparing Chicago Style Pepperoni Pizza Tossing dough... Adding sauce... Adding toppings: Shredded Mozzarella Cheese Black Olives Spinach Eggplant Sliced Pepperoni Bake for 25 minutes at 350 Cutting the pizza into square slices Place pizza in official PizzaStore box Joel ordered a Chicago Style Pepperoni Pizza --- Making a NY Style Veggie Pizza --- Preparing NY Style Veggie Pizza Tossing dough... Adding sauce... Adding toppings: Grated Reggiano Cheese Garlic Onion Mushrooms Red Pepper Bake for 25 minutes at 350 Cutting the pizza into diagonal slices Place pizza in official PizzaStore box Ethan ordered a NY Style Veggie Pizza --- Making a Chicago Deep Dish Veggie Pizza --- Preparing Chicago Deep Dish Veggie Pizza Tossing dough... Adding sauce... Adding toppings: Shredded Mozzarella Cheese Black Olives Spinach Eggplant Bake for 25 minutes at 350 Cutting the pizza into square slices Place pizza in official PizzaStore box Joel ordered a Chicago Deep Dish Veggie Pizza