外观模式：
为子系统中的一系列接口提供了一个统一的界面。外观模式定义了一个高层次的接口以使子系统更加easy使用。

Provide a unified interface to a set of interfaces in a subsystem.
Façade defines a higher-level interface that makes the subsystem easier to use.

UML图：

主要包含：

1. Facade(MortgageApplication)：了解每一个子系统负者的功能；将client的请求分发给合适的子系统。
2. SubSystem classes（Bank,Credit,Loan）:实现子系统的功能。处理Facade指定的业务，这个类中没有Facede类的信息。

C++代码实现：

#include <iostream>class SubSystem1
{public:void method1(){std::cout<<"SubSystem1::method1 invoke"<<std::endl;}
};class SubSystem2
{public:void method2(){std::cout<<"SubSystem2::method2 invoke"<<std::endl;}
};class SubSystem3
{public:void method3(){std::cout<<"SubSystem3::method3 invoke"<<std::endl;}
};class Facade
{public:Facade(){subSystem1=new SubSystem1();subSystem2=new SubSystem2();subSystem3=new SubSystem3();}void methodA(){std::cout<<"Facade methodA include:"<<std::endl;subSystem1->method1();subSystem2->method2();}void methodB(){std::cout<<"Facade methodB include:"<<std::endl;subSystem1->method1();subSystem3->method3();}~Facade(){if(subSystem1!=NULL)delete subSystem1;if(subSystem2!=NULL)delete subSystem2;if(subSystem3!=NULL)delete subSystem3;}private:SubSystem1 * subSystem1;SubSystem2 * subSystem2;SubSystem3 * subSystem3;
};int main()
{std::cout<<"外观模式測试"<<std::endl;Facade * facade=new Facade;facade->methodA();facade->methodB();delete facade;return 0;
}

运行结果：

一个详细的样例：

Facade为Morgage，这个类用来推断是否能对客户抵押贷款(依据客户的银行账户，行用卡记录，贷款记录来推断)。

SubSystem包含Bank(即客户的银行账户是否满足要求),Credit(客户的信用卡是否符合要求),Loan(客户的是否存在不良贷款记录)。

C++代码例如以下：

#include <iostream>
#include <stdlib.h>
#include <stdio.h>
#include <string>
using namespace std;
class Customer
{public:Customer(string str=""):name(str){}string getName() const{return name;}void setName(string str){name=str;}private:string name;};class Bank
{public:bool hasSufficientSavings(Customer c,int amount){std::cout<<"check bank for "<<c.getName()<<std::endl;return true;}
};class Credit
{public:bool hasGoodCredit(Customer c){std::cout<<"check credit for "<<c.getName()<<std::endl;return true;}
};class Loan
{public:bool hasNoBadLoans(Customer c){std::cout<<"check loans for "<<c.getName()<<std::endl;return true;}
};class Mortgage
{public:Mortgage(){bank=new Bank;credit=new Credit;loan=new Loan;}bool isEligible(Customer c, int amount){std::cout<<c.getName()<<" applies for "<<amount<<std::endl;bool eligible=true;if(!bank->hasSufficientSavings(c,amount)){eligible=false;}else if(!credit->hasGoodCredit(c)){eligible=false;}else if(!loan->hasNoBadLoans(c)){eligible=false;}return eligible;}~Mortgage(){if(!bank)delete bank;if(!credit)delete credit;if(!loan)delete loan;}private:Bank * bank;Credit *credit;Loan * loan;
};int main()
{std::cout<<"外观模式详细样例"<<std::endl;Mortgage *mortgage=new Mortgage();Customer c(string("John"));bool eligible =mortgage->isEligible(c,25000);std::cout<<c.getName()<<" has been "<<(eligible?

"approve":"reject")<<std::endl; return 0; }

运行结果：

外观模式是一个对迪米特法则非常好的应用。

迪米特法则：
假设两个类不必直接通信，那么这两个类就不应当发生直接的相互作用。假设当中一个类须要调用还有一个类的某一个方法的话。能够通过第三者转发这个调用。
这也是减少耦合性的思想。