【翻譯】設計模式之外觀（Facade）模式——C++實例

通常，隨着你的程序的不斷髮展，其複雜性也不斷增加。事實上，過多的使用設計模式致使大量的類被創建，從而導致程序流程難以理解。更有甚者，各個子系統都變得相當複雜，有大量複雜的接口。

外觀模式能幫助你簡化複雜的接口，它通過提供一系列簡單的接口給子系統，達到簡化的目的。這種簡化可能減少靈活性，但通常還是會提供底層控制給需要的用戶，如果需要，用戶仍然可以使用底層的類和方法。

外觀模式的使用頻率很高。

C++代碼示例：

//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; }

輸出：

更多關於 Facade:
http://sourcemaking.com/design_patterns/facade
http://www.patterndepot.com/put/8/facade.pdf
http://sourcemaking.com/design_patterns/facade

原文出處：http://advancedcppwithexamples.blogspot.com/ （被牆）