Simple Factory设计模式

一般我们要创建一个对象的时候，会使用new关键字来进行创建。但是，有时候，我们需要在程序运行的时候来动态决定创建哪个类的对象。比如：

public ParentClass doTask(int type){
ParentClass pc;
if(type > 0)
   pc = new ClassA();
else if(type = 0)
   pc = new ClassB();
else
   pc = new ClassC();

pc.do1();
pc.do2();
pc.do3();
}

那么，为了提高程序的可维护性和可扩展性，我们可以考虑将对象创建部分的逻辑单独提出来。

示例代码：

public class SimpleFactoryTest{
public static void main(String[] args){
SimplePizzaFactory factory = new SimplePizzaFactory();
PizzaStore store=new PizzaStore(factory);
store.orderPizza("cheese");
store.orderPizza("pepperoni");
store.orderPizza("clam");
}
}

class PizzaStore{
SimplePizzaFactory factory;
public PizzaStore(SimplePizzaFactory factory){
this.factory = factory;
}

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


class SimplePizzaFactory{
public Pizza createPizza(String type){
Pizza pizza=null;
if(type.equals("cheese"))
pizza=new CheesePizza();
else if(type.equals("pepperoni"))
pizza=new PepperoniPizza();
else if(type.equals("clam"))
pizza=new ClamPizza();
return pizza;
}
}

abstract class Pizza{
protected abstract void prepare();
protected abstract void bake();
protected abstract void cut();
protected abstract void box();
}

class CheesePizza extends Pizza{
public void prepare(){
System.out.println("CheesePizza prepared");
}
public void bake(){
System.out.println("CheesePizza baked");
}
public void cut(){
System.out.println("CheesePizza cutted");
}
public void box(){
System.out.println("CheesePizza boxed");
}
}

class PepperoniPizza extends Pizza{
public void prepare(){
System.out.println("PepperoniPizza prepared");
}
public void bake(){
System.out.println("PepperoniPizza baked");
}
public void cut(){
System.out.println("PepperoniPizza cutted");
}
public void box(){
System.out.println("PepperoniPizza boxed");
}
}

class ClamPizza extends Pizza{
public void prepare(){
System.out.println("ClamPizza prepared");
}
public void bake(){
System.out.println("ClamPizza baked");
}
public void cut(){
System.out.println("ClamPizza cutted");
}
public void box(){
System.out.println("ClamPizza boxed");
}
}

执行结果：
C:\javastudy>java SimpleFactoryTest
CheesePizza prepared
CheesePizza baked
CheesePizza cutted
CheesePizza boxed
PepperoniPizza prepared
PepperoniPizza baked
PepperoniPizza cutted
PepperoniPizza boxed
ClamPizza prepared
ClamPizza baked
ClamPizza cutted
ClamPizza boxed

C:\javastudy>