工厂模式

1. 定义
   工厂模式定义了一个创建对象的接口，但由子类决定实例化的类是哪一个。工厂模式方法让类把实例化推迟到子类。
2. 案例分析
   假设现在有一个比萨店。

Pizza orderPizza(String type){        Pizza pizza ;        if(type.equals("cheese"))            pizza = new CheesePizza();        else if(type.equals("greek"))            pizza = new GreekPizza();        pizza.prepare();        pizza.bake();        pizza.cut();        pizza.box();        return pizza;}

但是这样做会有一个问题，那就是当我们需要增加和改变pizza类型时必须修改该部分代码，违反了“对扩展开放，对修改关闭的原则”
所以我们可以这么做，

Pizza  PizzaStore{        Simplefactory  factory;        public PizzaStore(Simplefactory factory){                this.factory = factory;        }        Pizza orderPizza(String type){            Pizza pizza ;             pizza = factory.createPizza(type)            pizza.prepare();            pizza.bake();            pizza.cut();            pizza.box();            return pizza;}

进一步的，如果有多个工厂我们可以如下设计

package org.sxd.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;    }    abstract Pizza createPizza(String type);}

将PizzaStore设置成抽象类，那么子类就可以继承这个类，从而自定义ccreatePizza方法，依旧是不同的工厂了。
3. 实现

package org.sxd.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;    }    abstract Pizza createPizza(String type);}

package org.sxd.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");    }}

package org.sxd.factory;public class NYPizzaStore extends PizzaStore{    @Override    Pizza createPizza(String type) {        // TODO Auto-generated method stub        if(type.equals("cheese")){            return new NYStyleCheesePizza();        }        return null;    }}

package org.sxd.factory;import java.util.ArrayList;public class Pizza {    protected String name;    protected String dough;    protected String sauce;    ArrayList toppings = new ArrayList();    protected void prepare(){        System.out.println("Prepareing " + name);        System.out.println("Tossing dough...");        System.out.println("Adding sauce...");        System.out.println("Adding topping: ");        for(int i =0; i < toppings.size(); i++){            System.out.println("    " + toppings.get(i));        }    }    protected void bake(){        System.out.println("Bake for 25 minutes at 350");    }    protected void cut(){        System.out.println("Cutting the pizza into diagonal slices");    }    protected void box(){        System.out.println("Please pizza in offical PizzaStore Box");    }    public String getName(){        return name;    }}

package org.sxd.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");    }    protected void cut(){        System.out.println("Cutting the pizza into square slices");    }}

package org.sxd.factory;public class ChicagoPizzaStore extends PizzaStore{    @Override    Pizza createPizza(String type) {        // TODO Auto-generated method stub        if(type.equals("cheese")){            return new ChicagoStyleCheesePizza();        }        return null;    }}

package org.sxd.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");    }}