【翻译】设计模式之外观（Facade）模式——C++实例

通常，随着你的程序的不断发展，其复杂性也不断增加。事实上，过多的使用设计模式致使大量的类被创建，从而导致程序流程难以理解。更有甚者，各个子系统都变得相当复杂，有大量复杂的接口。

外观模式能帮助你简化复杂的接口，它通过提供一系列简单的接口给子系统，达到简化的目的。这种简化可能减少灵活性，但通常还是会提供底层控制给需要的用户，如果需要，用户仍然可以使用底层的类和方法。

外观模式的使用频率很高。

C++代码示例：

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy //Façade is part of Structural Patterns //Structural Patterns deal with decoupling the interface and implementation of classes and objects //A Facade is single class that represents an entire subsystem //The example we consider here is a case of a customer applying for mortgage //The bank has to go through various checks to see if Mortgage can be approved for the customer //The facade class goes through all these checks and returns if the morgage is approved #include<iostream> #include<string> using namespace std; // Customer class class Customer { public: Customer (const string& name) : name_(name){} const string& Name(void) { return name_; } private: Customer(); //not allowed string name_; }; // The 'Subsystem ClassA' class class Bank { public: bool HasSufficientSavings(Customer c, int amount) { cout << "Check bank for " <<c.Name()<<endl; return true; } }; // The 'Subsystem ClassB' class class Credit { public: bool HasGoodCredit(Customer c, int amount) { cout << "Check credit for " <<c.Name()<<endl; return true; } }; // The 'Subsystem ClassC' class class Loan { public: bool HasGoodCredit(Customer c, int amount) { cout << "Check loans for " <<c.Name()<<endl; return true; } }; // The 'Facade' class class Mortgage { public: bool IsEligible(Customer cust, int amount) { cout << cust.Name() << " applies for a loan for $" << amount <<endl; bool eligible = true; eligible = bank_.HasSufficientSavings(cust, amount); if(eligible) loan_.HasGoodCredit(cust, amount); if(eligible) credit_.HasGoodCredit(cust, amount); return eligible; } private: Bank bank_; Loan loan_; Credit credit_; }; //The Main method int main() { Mortgage mortgage; Customer customer("Brad Pitt"); bool eligible = mortgage.IsEligible(customer, 1500000); cout << "/n" << customer.Name() << " has been " << (eligible ? "Approved" : "Rejected") << endl; return 0; }

输出：

更多关于 Facade:
http://sourcemaking.com/design_patterns/facade
http://www.patterndepot.com/put/8/facade.pdf
http://sourcemaking.com/design_patterns/facade

原文出处：http://advancedcppwithexamples.blogspot.com/ （被墙）