Skip to main content

The Facade pattern

Facade design pattern is a structural design pattern and it's used widely. The aim of this design pattern is to provide a simple interface to the client for a complex underlying system. So, facade means face of the building. This design pattern hides all complexities of the system and just displays a simple face. Very common example could be URL interface of a browser, which hides all complexities behind and only accepts a URL which user intends to browse. Another common example could be withdrawal / deposit of money from banking system via ATM.

To withdraw money we need following steps to achieve successfully:

1. Validate card / account number

2. Validate pin

3. In case of withdrawal check account balance and allow / disallow withdrawal

4. Follow steps 1 & 2 for account deposit (Steps 3 not needed).

5. Finally show the balance.


Code Example: 

<Code>

File: WelcomeBank.h

#pragma once
#include <fmt/format.h>

class WelcomeBank{
    public:
        // ctor...
        WelcomeBank(){
            fmt::print("{}\n", "Welcome to ABC Bank");
        }

};

File: AccountNumberCheck.h

class AccountNumberCheck {
    private:
        unsigned int _acctNumber = 12345678;
    public:
         unsigned int getAccountNumber() { return _acctNumber; }
         bool isAccountActive(unsigned int accountNumber)
         {
             if(getAccountNumber() == accountNumber) return true;
             else return false;
         }
};

File: SecurityCodeCheck.h

#pragma once
class SecurityCodeCheck{
    private:
        unsigned int _securityCode = 1234;
    public:
         unsigned int getSecurityCode() { return _securityCode; }
         bool isCodeCorrect(unsigned int securityCodeToCheck)
         {
             if(getSecurityCode() == securityCodeToCheck)
                return true;
             else
                return false;
         }
};

File: FundsCheck.h

#pragma once
#include <fmt/format.h>

class FundsCheck {
    double cashInAccount = 1000.00;
    void decreaseCashInAccount(double cashWithDrawn) {
            cashInAccount -= cashWithDrawn;
        }

        void increaseCashInAccount(double cashDeposited) {
            cashInAccount += cashDeposited;
        }
    public:
        double getCashInAccount() {
            return cashInAccount;
        }

        bool haveEnoughMoney(double cashWithDrawal) {
            if(cashWithDrawal > getCashInAccount()) {
                fmt::print("Error: Don't have enough balanace!\n");
                fmt::print("Current Balance: {}\n", getCashInAccount());
                return false;
            }
            else {
                decreaseCashInAccount(cashWithDrawal);
                fmt::print("Withdrawal complete, New Balance is: {}\n", getCashInAccount());
                return true;
            }
        }

        void makeDeposits(double cashToDeposit){
            increaseCashInAccount(cashToDeposit);
            fmt::print("Deposit complete, new balance is: {}\n", getCashInAccount());
        }
};

File: BankAccountFacade.h

/* This is our facade implementation */
#include "AccountNumberCheck.h"
#include "FundsCheck.h"
#include "SecurityCodeCheck.h"
#include "WelcomeBank.h"

class BankAccountFacade{
    private:
        unsigned int _accountNumber;
        unsigned int _securityCode;

        AccountNumberCheck accCheker;
        SecurityCodeCheck codeChecker;
        FundsCheck fundCheker;

    public:
        BankAccountFacade(int accNum, int secCode) :
            _accountNumber(accNum),
            _securityCode(secCode) {}
        unsigned int getAccountNumber() { return _accountNumber; }
        unsigned int getSecurityCode() { return _securityCode; }

        void withdrawCash(double cashToGet) {
           
            WelcomeBank bankGreet;
            if(accCheker.isAccountActive(getAccountNumber()) &&
                codeChecker.isCodeCorrect(getSecurityCode()) &&
                fundCheker.haveEnoughMoney(cashToGet)) {
                    fmt::print("Transaction complete\n");
                }
                else
                    fmt::print("Transaction failed\n");
        }

        void depositCash(double cashToDeposit) {
            WelcomeBank bankGreet;

            if(accCheker.isAccountActive(getAccountNumber()) &&
                codeChecker.isCodeCorrect(getSecurityCode())) {
                    fundCheker.makeDeposits(cashToDeposit);
                    fmt::print("Transaction complete\n");
                }
                else
                    fmt::print("Transaction failed\n");
        }
};

// This part contains our client code
File: example.cpp

#include "BankAccountFacade.h"
int main()
{
    BankAccountFacade accessingBank(12345678, 1234);
    accessingBank.withdrawCash(50.00);
    accessingBank.withdrawCash(900.00);
    accessingBank.depositCash(50.00);
    return 0;
}

</Code> 

Demo (Compiler Explorer code)

Credit: Design Patterns: Elements of Reusable Object-Oriented Software (by GoF)

Labels:

Comments

Post a Comment

Popular posts from this blog

Variadic template class to add numbers recursively during compilation

 The idea of having a class to add numbers (variable parameters) during compilation time recursively. Also wanted to restrict types to a single type while sending parameters to class member function. That said, if we mix int, float and double types to add function shall result in compilation error. How do we achieve this. The below is the code which actually helps to achieve this: <code> #include < fmt/format.h > template < typename T> class MyVarSumClass{     private :         T _sum = 0 ;     public :         template < typename ... TRest>         T add(T num, TRest... nums){             static_assert (std::conjunction<std::is_same<TRest, T>...>{}); /* Assert fails                if types are different */             _sum += num;             return add(nums...); // Next parameter packs gets picked recursively         }         // Base case         T add(T num){             _sum += num;             return _sum;         } }; int main() {     My
Post a Comment
Read more

A simple approach to generate Fibonacci series via multi-threading

T his is a very simple approach taken to generate the Fibonacci series through multithreading. Here instead of a function, used a function object. The code is very simple and self-explanatory.  #include <iostream> #include <mutex> #include <thread> class Fib { public:     Fib() : _num0(1), _num1(1) {}     unsigned long operator()(); private:     unsigned long _num0, _num1;     std::mutex mu; }; unsigned long Fib::operator()() {     mu.lock(); // critical section, exclusive access to the below code by locking the mutex     unsigned long  temp = _num0;     _num0 = _num1;     _num1 = temp + _num0;     mu.unlock();     return temp; } int main() {     Fib f;          int i = 0;     unsigned long res = 0, res2= 0, res3 = 0;     std::cout << "Fibonacci series: ";     while (i <= 15) {         std::thread t1([&] { res = f(); }); // Capturing result to respective variable via lambda         std::thread t2([&] { res2 = f(); });         std::thread t3(
Post a Comment
Read more

A concept to a product (Kimidori [ 黄緑]) - Part 2

In the previous part , we have seen KIMIDORI [ 黄緑] detect if a URL is malicious. In this part, we will see the details that KIMIDORI [ 黄緑] fetches out of the URL provided. As an example, provided a safe URL, https://www.azuresys.com/, and let's see what it brings out: As we can see, the link is safe and the link is active, which means we can just click on the link to open it on IE.  Now it's time to look into the URL report (still under development):  We have URLs IP, Location, and HTTP Status code. The Report part is a sliding window, the Show Report button shows as well as hides the report. Show / Hide Report is a toggle button. Let's see if we get the same details for any bad (phishing / malicious) URL: Took an URL example from a phishing link and tested it. The tool detected it as not a good link (Screen Shot Below) & link does not activate unlike a safe URL: Now let's see the report part for more details including domain registration details: It looks like it&
Post a Comment
Read more