Strategy Design Pattern define a family of algorithms, encapsulate each one, and make then interchangeable. Strategy lets the algorithm vary independently from clients that use it.
Class Diagram:
Class Diagram of real example:
Source Code of real example in C++:
/*
* File:strategy.cpp
* This file is described the strategy Design Pattern with help of example
* Strategy pattern is structutal Pattern
* Author: Aplha
* Date: 31 Dec 2020
*/
//Header File
#include<iostream>
//TreadMill Class (Base class of different strategy)
class TreadMillStrategy
{
protected:
int m_speed;
public:
virtual void Start() = 0;
virtual void Stop() = 0;
};
class ChildStrategy:public TreadMillStrategy
{
public:
ChildStrategy(int speed){ m_speed = speed;}
~ChildStrategy(){}
void Start()
{
if(SpeedRestriction())
{
std::cout<<"Child TreadMill Mode Started, speed:"<<m_speed<<std::endl;
//Call the Driver api to start the Motor
}
else
{
std::cout<<"Child TreadMill Mode Cannot start, speed is more"<<std::endl;
}
}
void Stop() {std::cout<<"Child TreadMill Mode Stop"<<std::endl;}
private:
bool SpeedRestriction()
{ return (m_speed < 10) ? true : false;}
};
//Adult TreadMill Mode
class AdultStrategy:public TreadMillStrategy
{
public:
AdultStrategy(int speed){ m_speed = speed; }
~AdultStrategy(){}
void Start()
{
std::cout<<"Adult TreadMill Mode Started, speed:"<<m_speed<<std::endl;
IncreaseSpeed();
std::cout<<"Adult TreadMill Mode speed increased, speed:"<<m_speed<<std::endl;
}
void Stop() {std::cout<<"Adult TreadMill Mode Stop"<<std::endl;}
private:
void IncreaseSpeed()
{ m_speed = m_speed + 10;}
};
//Controller
class Controller
{
TreadMillStrategy* m_st;
public:
Controller(TreadMillStrategy* tm): m_st(tm){}
~Controller(){}
void SetStrategy(TreadMillStrategy* tr)
{
m_st = tr;
std::cout<<"*************Changing Strategy at run tim*************"<<std::endl;
}
void StartInterface(){m_st->Start();}
void StopInterface(){m_st->Stop();}
};
//CLient
int main()
{
// Strategy Pattern is Structutal Pattern so
// Inside Controller we will not create of TreaMillStrategy
// Below creation of different strategy can be done by Factory Pattern
// Creation of different strategy is depend upon Client(HOw is using strategy)
std::cout<<"Strategy Design Pattern"<<std::endl;
TreadMillStrategy* tm = new ChildStrategy(5);
Controller* con = new Controller(tm);
con->StartInterface();
con->StopInterface();
///////////////////////Change Strategy at run time;
delete tm;
tm = new AdultStrategy(10);
con->SetStrategy(tm);
con->StartInterface();
con->StopInterface();
delete tm;
delete con;
return 0;
}
Compilation Command:
g++ -std=c++11 strategy.cpp
Output:
Strategy Design Pattern
Child TreadMill Mode Started, speed:5
Child TreadMill Mode Stop
*************Changing Strategy at run tim*************
Adult TreadMill Mode Started, speed:10
Adult TreadMill Mode speed increased, speed:20
Adult TreadMill Mode Stop