设计模式——工厂方法模式

4.

OO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。

例子：披萨店的披萨生产

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;
}
}

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;
}
}

import java.util.ArrayList;

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

void prepare() {
System.out.println("Prepare " + name);
System.out.println("Tossing dough...");
System.out.println("Adding sauce...");
System.out.println("Adding toppings: ");
for (String topping : toppings) {
System.out.println("   " + topping);
}
}

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

void cut() {
System.out.println("Cut 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 (String topping : toppings) {
display.append(topping + "\n");
}
return display.toString();
}
}

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;
}
}

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");
}
}

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");
}
}

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");
}
}