深入浅出设计模式四——比萨店生产比萨实现(工厂方法模式）

在http://quicker.iteye.com/blog/571714一文中已经讲了简单工厂和工厂方法并且有UML图和实现的代码。

这里只结合实例分析一下工厂方法在实际生活中的应用。

我们看看比萨店及比萨的图。

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产品图。

结合http://quicker.iteye.com/blog/571714中关于工厂方法模式的实现，不难得出实现代码：

package com.lwf.disign.learn.factorymethod;public abstract class PizzaStore {public final Pizza orderPizza(String type){Pizza pizza;pizza = createPizza(type);pizza.prepare();pizza.bake();pizza.cut();pizza.box();return pizza;}abstract Pizza createPizza(String type);}

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package com.lwf.disign.learn.factorymethod;public class NYPizzaStore extends PizzaStore {Pizza createPizza(String type) {Pizza pizza = null;if(type.equals("cheese")){pizza = new NYCheesePizza();}else if(type.equals("veggle")){pizza = new NYVegglePizza();}return pizza;}}

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package com.lwf.disign.learn.factorymethod;public class ChicagoPizzaStore extends PizzaStore {Pizza createPizza(String type) {Pizza pizza = null;if(type.equals("cheese")){pizza = new ChicagoCheesePizza();}else if(type.equals("veggle")){pizza = new ChicagoVegglePizza();}return pizza;}}

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package com.lwf.disign.learn.factorymethod;import java.util.ArrayList;public abstract class Pizza {String name;//名称String dough;//面团类型String sauce;//酱料类型ArrayList toppings = new ArrayList(); //一套佐料public void prepare() {System.out.println("Preparing " + name);System.out.println("Tossign dough..." + dough);System.out.println("Adding sauce..." + sauce);System.out.println("Adding toppings: ");for (int i = 0; i < toppings.size(); i++) {System.out.println(" " + toppings.get(i));}}public void bake() {System.out.println("Bake for 25 minutes at 350");}public void cut() {System.out.println("Cutting the pizza into diagonal slices");}public void box() {System.out.println("Pizza in offical PizzaStrore box");}public String getName(){return name;}}

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package com.lwf.disign.learn.factorymethod;public class NYCheesePizza extends Pizza {public NYCheesePizza(){name = "NYCheesePizza";dough = "Thin crust dough NYCheesePizza";sauce = "Marina sauce NYCheesePizza";toppings.add("Grated NYCheesePizza cheese");}public void cut(){System.out.println("cut it into NYCheesePizza slices");}}

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package com.lwf.disign.learn.factorymethod;public class NYVegglePizza extends Pizza {public NYVegglePizza(){name = "NYVegglePizza";dough = "Thin crust dough NYVegglePizza";sauce = "Marina sauce NYVegglePizza";toppings.add("Grated NYVegglePizza cheese");}public void cut(){System.out.println("cut it into NYVegglePizza slices");}}

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package com.lwf.disign.learn.factorymethod;public class ChicagoCheesePizza extends Pizza {public ChicagoCheesePizza(){name = "ChicagoCheesePizza";dough = "Thin crust dough ChicagoCheesePizza";sauce = "Marina sauce ChicagoCheesePizza";toppings.add("Grated ChicagoCheesePizza cheese");}public void cut(){System.out.println("cut it into ChicagoCheesePizza slices");}}

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package com.lwf.disign.learn.factorymethod;public class ChicagoVegglePizza extends Pizza {public ChicagoVegglePizza(){name = "ChicagoVegglePizza";dough = "Thin crust dough ChicagoVegglePizza";sauce = "Marina sauce ChicagoVegglePizza";toppings.add("Grated ChicagoVegglePizza cheese");}public void cut(){System.out.println("cut it into ChicagoVegglePizza slices");}}

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上面共定义了四种比萨，客户向系统订购这四种比萨。。

package com.lwf.disign.learn.factorymethod;public class PizzaStoreTest {public static void main(String[] args) {PizzaStore pizzaStore = new NYPizzaStore();Pizza pizza = pizzaStore.orderPizza("cheese");print(pizza.getName());pizza = pizzaStore.orderPizza("veggle");print(pizza.getName());pizzaStore = new ChicagoPizzaStore();pizza = pizzaStore.orderPizza("cheese");print(pizza.getName());pizza = pizzaStore.orderPizza("veggle");print(pizza.getName());}public static void print(String name){System.out.println(name);System.out.println("-------------------------");}}

?输出结果为：

Preparing NYCheesePizzaTossign dough...Thin crust dough NYCheesePizzaAdding sauce...Marina sauce NYCheesePizzaAdding toppings:  Grated NYCheesePizza cheeseBake for 25 minutes at 350cut it into NYCheesePizza slicesPizza in offical PizzaStrore boxNYCheesePizza-------------------------Preparing NYVegglePizzaTossign dough...Thin crust dough NYVegglePizzaAdding sauce...Marina sauce NYVegglePizzaAdding toppings:  Grated NYVegglePizza cheeseBake for 25 minutes at 350cut it into NYVegglePizza slicesPizza in offical PizzaStrore boxNYVegglePizza-------------------------Preparing ChicagoCheesePizzaTossign dough...Thin crust dough ChicagoCheesePizzaAdding sauce...Marina sauce ChicagoCheesePizzaAdding toppings:  Grated ChicagoCheesePizza cheeseBake for 25 minutes at 350cut it into ChicagoCheesePizza slicesPizza in offical PizzaStrore boxChicagoCheesePizza-------------------------Preparing ChicagoVegglePizzaTossign dough...Thin crust dough ChicagoVegglePizzaAdding sauce...Marina sauce ChicagoVegglePizzaAdding toppings:  Grated ChicagoVegglePizza cheeseBake for 25 minutes at 350cut it into ChicagoVegglePizza slicesPizza in offical PizzaStrore boxChicagoVegglePizza-------------------------

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设计原则：要依赖抽象，不要依赖具体类，也叫依赖倒置原则

如下图：

?可以看到上下都依赖于pizza这个抽象类..

?这启发我们思考方式的变化，我们也可以倒置思考方式：如一般你想开个比萨店先会想到要用什么做比萨，考虑一大堆原料等。。。最后才是比萨店。那么我们可以改变思考的方式，我们只需要把比萨先做一个抽象。那们上我们可以开比萨店，下我们可以制作多种类型的比萨。

下面有几种方式可以让我们尽可能的遵守倒置原则

然而上面的三点要求对待程序可谓是严格的。。当然如果一个类以后变化的机会很少，那么为什么不直接new出来呢。如String类。。所以这些都只是让我们的设计变得更好的方针，不能死套在程序上。