Design-Pattern/Design Pattern 3 of 3.html at master · mathetian/Design-Pattern · GitHub

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<head>
	<title>Design Pattern 2 of 3</title>
	<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=utf-8">
</head>
<body>
<h1>Behavioral</h1>
	到了一个新的话题了，These patterns characterize complex control flow that's difficult to follow at run-time. They shift your focus away from flow of control to let you concentrate <span style="color:red">just on</span> the way objects are interconnected.

	A behavioral pattern explains how objects interact. It describes how different objects and classes send messages to each other to make things happen and how the steps of a task are divided among different objects.

	个人感觉这个部分主要就是you belong to me & me belong to you. 在CTP中就有这个东东.

<h2>Chain of Responsibility</h2>
	The chain of responsibility pattern is a design pattern that defines a linked list of handlers, each of which is able to process requests.

	其实就是一个event_proxy_handler。有点类似于前段时间遇到过的话务员问题。
	[sourcecode language="c"]
	#include <iostream>

	//Not very good example
	class HandlerBase{
	public:
		HandlerBase(){};
		virtual ~ HandlerBase(){};
		virtual void setNext(HandlerBase*next)
		{
			_next=next;
		}
		virtual void HandlerMsg(int level)=0;
	protected:
		HandlerBase*_next;
	};

	class ConcreteHandlerA:public HandlerBase{
	public:
		ConcreteHandlerA(){};
		virtual ~ ConcreteHandlerA(){};
		virtual void HandlerMsg(int level)
		{
			if(level==1)
				std::cout<<"ConcreteHandlerA handler"<<std::endl;
			else _next->HandlerMsg(level);
		}
	};

	class ConcreteHandlerB:public HandlerBase{
	public:
		ConcreteHandlerB(){};
		virtual ~ ConcreteHandlerB(){};
		virtual void HandlerMsg(int level)
		{
			if(level==2)
				std::cout<<"ConcreteHandlerB handler"<<std::endl;
			else _next->HandlerMsg(level);
		}
	};

	class ConcreteHandlerC:public HandlerBase{
	public:
		ConcreteHandlerC(){};
		virtual ~ ConcreteHandlerC(){}
		virtual void HandlerMsg(int level)
		{
			if(level==3)
				std::cout<<"ConcreteHandlerC handler"<<std::endl;
			else _next->HandlerMsg(level);
		}
	};

	int main()
	{
		HandlerBase*a=new ConcreteHandlerA();
		HandlerBase*b=new ConcreteHandlerB();
		HandlerBase*c=new ConcreteHandlerC();
		a->setNext(b);b->setNext(c);
		a->HandlerMsg(1);
		a->HandlerMsg(2);
		a->HandlerMsg(3);
		delete a;delete b;delete c;
		return 0;
	}
	[/sourcecode]

<h2>Command</h2>
	The command pattern is a design pattern that enables all of the information for a request to be contained within a single object.

	Four elements in it,
	<ul>
		<li>Client: main</li>
		<li>Receiver: Robot</li>
		<li>CommandBase: It holds information about the receiver.</li>
		<li>ConcreteCommand</li>
		<li>Invoker: controller</li>
	</ul>

	Use the Command pattern when you want to:
	<ul>
		<li>parameterize objects by an action to perform</li>
		<li>specify, queue, and execute requests at different times.</li>
		<li>support undo</li>
		<li>support logging changes so that they can be reapplied in case of a system crash.</li>
		<li>structure a system around high-level operations built on primitives operations.</li>
	</ul>

	<span style="color:red">这个部分完全不知道怎么理解. The relationship between objects is hard to understand.</span>

	命令（Command）模式属于对象的行为模式。命令模式又称为行动（Action）模式或交易（Transaction）模式。命令模式把一个请求或者操作封装到一个对象中。命令模式允许系统使用不同的请求把客户端参数化，对请求排队或者记录请求日志，可以提供命令的撤销和恢复功能。

	命令模式是对命令的封装。命令模式把发出命令的责任和执行命令的责任分割开，委派给不同的对象。

	每一个命令都是一个操作：请求的一方发出请求要求执行一个操作；接收的一方收到请求，并执行操作。命令模式允许请求的一方和接收的一方独立开来，使得请求的一方不必知道接收请求的一方的接口，更不必知道请求是怎么被接收，以及操作是否被执行、何时被执行，以及是怎么被执行的。

	<span style="color:red">callback function, that is, a function that's registered somewhere to be called at a later point.</span>
	[sourcecode language="c"]
	#include <iostream>
	#include <vector>
	//Like the example of website
	class Robot{
	public:
		Robot(){position=0;}
		~ Robot(){}
		void moveLeft(int flag)
		{
			if(flag==1) position-=1;
			else position+=1;
			if(flag==1)
				std::cout<<"excute LeftMovement:"<<position<<std::endl;
			else
				std::cout<<"undo LeftMovement:"<<position<<std::endl;
		}
		void moveRight(int flag)
		{
			if(flag==1) position+=1;
			else position-=1;
			if(flag==1)
				std::cout<<"excute RightMovement:"<<position<<std::endl;
			else
				std::cout<<"undo RightMovement:"<<position<<std::endl;
		}
	private:
		int position;
	};

	class Movement{
	public:
		Movement(Robot*robot):robot(robot){}
		virtual ~ Movement(){}
		virtual void excute(int flag)=0;
	public:
		Robot*robot;
	};

	class Controller{
	public:
		void excute(Movement*a)
		{
			vCommands.push_back(a);
			a->excute(1);
		}
		void undo()
		{

			Movement*cur=vCommands[vCommands.size()-1];
			cur->excute(0);
			vCommands.pop_back();
		}
	private:
		std::vector<Movement*>vCommands;
	};


	class LeftMovement:public Movement{
	public:
		LeftMovement(Robot*robot):Movement(robot){}
		virtual ~ LeftMovement(){}
		virtual void excute(int flag)
		{
			robot->moveLeft(flag);
		}
	};

	class RightMovement:public Movement{
	public:
		RightMovement(Robot*robot):Movement(robot){}
		virtual ~ RightMovement(){}
		virtual void excute(int flag)
		{
			robot->moveRight(flag);
		}
	};

	int main()
	{
		Robot*robot=new Robot();
		Movement*a=new LeftMovement(robot);
		Movement*b=new RightMovement(robot);
		Movement*c=new LeftMovement(robot);
		Movement*d=new RightMovement(robot);
		Controller*ctl=new Controller();
		ctl->excute(a);ctl->excute(c);
		ctl->excute(d);ctl->excute(b);

		ctl->undo();
		ctl->undo();
		return 0;
	}
	[/sourcecode]

<h2>Interpreter</h2>
	The interpreter pattern is a design pattern that is useful when developing domain-specific languages or notations. The pattern allows the grammar for such a notation to be represented in an object-oriented fashion that can easily be extended(What is it?).

	The Interpreter pattern is very similar to the Composite pattern. Like leaf and son.

	The interpreter pattern can solve string match(regex problem)?

	Elements:
	<ul>
		<li>AbstractExpression</li>
		<li>TerminalExpression</li>
		<li>NonterminalExpression</li>
		<li>Context</li>
		<li>Client</li>
	</ul>

	The real world example in <a href="http://www.codeproject.com/Articles/455228/Design-Patterns-3-of-3-Behavioral-Design-Patterns">website</a> is very good.

	[sourcecode language="c"]
	//One Algorithm question: interpreter for, + - + - - 2 3 4 + - -5 6 + -7 8 9 10

	//Some thing wrong for example
	#include <iostream>
	#include <queue>
	#include <string>

	class Expression{
	public:
		Expression(){}
		virtual int Excute()=0;
	};

	class TerminalExpresion:public Expression{
	public:
		TerminalExpresion(int value):value(value){}
		virtual int Excute()
		{
			std::cout<<value<<std::endl;
			return value;
		}
	private:
		int value;
	};

	class AddExpresion:public Expression{
	public:
		AddExpresion(Expression*_l,Expression*_r):_l(_l),_r(_r){}
		virtual int Excute()
		{
			std::cout<<"plus"<<std::endl;
			return _l->Excute()+_r->Excute();
		}
	private:
		Expression*_l;
		Expression*_r;
	};

	class MinusExpresion:public Expression{
	public:
		MinusExpresion(Expression*_l,Expression*_r):_l(_l),_r(_r){}
		virtual int Excute(){
			std::cout<<"minus"<<std::endl;
			return _l->Excute()-_r->Excute();
		}
	private:
		Expression*_l;
		Expression*_r;
	};


	class MultiplyExpression:public Expression{
	public:
		MultiplyExpression(Expression*_l,Expression*_r):_l(_l),_r(_r){}
		virtual int Excute()
		{
			return _l->Excute()*_r->Excute();
		}
	private:
		Expression*_l;
		Expression*_r;
	};

	class DivideExpression:public Expression{
	public:
		DivideExpression(Expression*_l,Expression*_r):_l(_l),_r(_r){}
		virtual int Excute()
		{
			return _l->Excute()/_r->Excute();
		}
	private:
		Expression*_l;
		Expression*_r;
	};

	class Parser{
	public:
		Expression*parse(std::queue<char>&str)
		{
			if(str.empty()) return NULL;
			while(isspace(str.front())) str.pop();
			if(str.empty()) return NULL;
			if(isDigital(str.front())==1)
				return new TerminalExpresion(getValue(str));
			parseOP(str);
		}

		Expression*parseOP(std::queue<char>&str)
		{
			if(str.empty()) return NULL;
			while(isspace(str.front())) str.pop();
			if(str.empty()) return NULL;

			switch(str.front())
			{
			case '+':
				str.pop();
				return new AddExpresion(parse(str),parse(str));
			case '-':
				str.pop();
				return new MinusExpresion(parse(str),parse(str));
			case '*':
				str.pop();
				return new MultiplyExpression(parse(str),parse(str));
			case '/':
				str.pop();
				return new DivideExpression(parse(str),parse(str));
			}
		}

		Expression*parse(std::string strs)
		{
			int len=strs.size();
			int i=0;std::queue<char>str;
			while(i<len)
			{
				str.push(strs[i]);
				i++;
			}
			return parse(str);
		}
	private:
		int getValue(std::queue<char>&str)
		{
			int value=0;
			while(!str.empty()&&!isspace(str.front()))
			{
				value=value*10+str.front()-'0';
				str.pop();
			}
			return value;
		}

		int isDigital(char flag)
		{
			if(flag>='0'&&flag<='9')
				return 1;
			return 0;
		}
	};

	int main()
	{
		Parser*p=new Parser();
		Expression*exp=p->parse("+ - 4 5 6");
		std::cout<<exp->Excute()<<std::endl;
		return 0;
	}
	[/sourcecode]

	<span style="color:red">I have look for the example in the book. A very similar example of previous. Many technologies are very good.</span>

<h2>Iterator</h2>
	Provides a means for the elements of an aggregate object to be accessed sequentially <span style="color:red">without knowledge of its structure</span>. This allows traversing of lists, trees and other structures in a standard manner.

	The main intent of the iterator pattern is to provide a simple interface for traversing a collection of items.

	The iterator object will maintain the state of the iteration, keeping track of the current item and having a way of identifying what elements are next to be iterated.

	Just like Iterator. <span style="color:red">The implement of iterator</span>. Some design principle in book are very good.

	[sourcecode language="c"]
	#include <iostream>
	#include <vector>

	template<class Item> class Iterator;

	template<class Item>
	class List{
	public:
		void add(Item item)
		{
			itemVec.push_back(item);
		}

		Iterator<Item>*begin()
		{
			return new Iterator<Item>(this);
		}
		int getSize()
		{
			return itemVec.size();
		}
		Item getElem(int index)
		{
			if(itemVec.size()<=index)
				return Item(0);
			return itemVec.at(index);
		}
	private:
		std::vector<Item>itemVec;
	};

	template<class Item>
	class Iterator{
	public:
		Iterator(){index=-1;}
		Iterator(List<Item>*pList):pList(pList){index=-1;}
		virtual ~ Iterator(){}
		Item Next()
		{
			index++;
			return pList->getElem(index);
		}
		Item Empty()
		{
			return pList->getElem(0);
		}
	private:
		List<Item>*pList;
		int index;
	};

	int main()
	{
		List<int> iLists;
		iLists.add(8);iLists.add(2);
		iLists.add(3);iLists.add(5);
		iLists.add(4);iLists.add(6);
		Iterator<int>*iterator=iLists.begin();
		while(1)
		{
			int elem=iterator->Next();
			if(elem==0) break;
			std::cout<<elem<<std::endl;
		}
	}
	[/sourcecode]

	 <span style="color:red">正如strcpy一样，实现的细节值得深入思考.</span>

<h2>Mediator</h2>
	Instead, mediator objects are used to encapsulate and centralize the interactions between classes.

	Very strange, can build a very beautiful system. Like p2p system.

	<span style="color:red">有几个例子可以理解这个模式，飞机调度系统以及excel中数据变化，barchat就会对应的有所变化</span>

	[sourcecode language="c"]
	#include <iostream>
	#include <vector>

	class MediatorBase;

	class ColleagueBase{
	public:
		virtual void change(){};
		virtual void notify(std::string str){};
		ColleagueBase(MediatorBase*mb);
	protected:
		MediatorBase*mb;
	};

	class MediatorBase{
	public:
		MediatorBase(){}
		void add(ColleagueBase*cb)
		{
			pcList.push_back(cb);
		}
		void notify(std::string str,ColleagueBase*cb)
		{
			for(int i=0;i<pcList.size();i++)
			{
				if(pcList[i]==cb) continue;
				pcList[i]->notify("MediatorBase");
			}
		}
	private:
		std::vector<ColleagueBase*> pcList;
	};

	ColleagueBase::ColleagueBase(MediatorBase*mb)
	{
		this->mb=mb;
		this->mb->add(this);
	}

	class CCA:public ColleagueBase{
	public:
		CCA(MediatorBase*mb):ColleagueBase(mb){}
		virtual void change()
		{
			std::cout<<"CCA changed"<<std::endl;
			mb->notify("CCA",this);
		}
		virtual void notify(std::string str)
		{
			std::cout<<str<<" CCA notified"<<std::endl;
		}
	};

	class CCB:public ColleagueBase{
	public:
		CCB(MediatorBase*mb):ColleagueBase(mb){}
		virtual void change()
		{
			std::cout<<"CCB changed"<<std::endl;
			mb->notify("CCB",this);
		}
		virtual void notify(std::string str)
		{
			std::cout<<str<<" CCB notified"<<std::endl;
		}
	};

	class CCC:public ColleagueBase{
	public:
		CCC(MediatorBase*mb):ColleagueBase(mb){}
		virtual void change()
		{
			std::cout<<"CCC changed"<<std::endl;
			mb->notify("CCC",this);
		}
		virtual void notify(std::string str)
		{
			std::cout<<str<<" CCC notified"<<std::endl;
		}
	};


	int main()
	{
		MediatorBase*mb=new MediatorBase();
		ColleagueBase*a=new CCA(mb);ColleagueBase*b=new CCB(mb);
		ColleagueBase*c=new CCC(mb);

		ColleagueBase*d=new CCA(mb);ColleagueBase*e=new CCB(mb);
		ColleagueBase*f=new CCC(mb);

		b->change();

		delete mb;delete a,b,c,d,e,f;
		return 0;
	}
	[/sourcecode]

<h2>Memento</h2>
	It is sometimes necessary to capture the internal state of an object at some point in time and have the ability to restore that state later at run time.

	This is the right place where you can use the memento pattern.

	This pattern is used to provide an application the undo functionality. Sometimes it is called undo with rollback.

	Undo, Redo.

	<span style="color:red">和前面的一个redo,undo的例子(哪个?)有些相似的地方.</span>
	[sourcode language="c"]
	#include <iostream>

	class Element{
	public:
		Element(int a,int b):a(a),b(b){}
		int ga(){return a;}
		int gb(){return b;}
	private:
		int a,b;
	};

	class Memento{
	public:
		Memento(Element e):e(e){}
		int ga(){return e.ga();}
		int gb(){return e.gb();}
	private:
		Element e;
	};


	class Originator{
	public:
		Originator(){_a=0;_b=0;}
		void add()
		{
			std::cout<<_a<<" "<<_b<<std::endl;
			_a++;
		}
		Memento*createMO()
		{
			Element e(_a,_b);
			return new Memento(e);
		}
		void set(Memento*mo)
		{
			_a=mo->ga();
			_b=mo->gb();
		}
	private:
		int _a,_b;
	};


	class Caretaker{
	public:
		Caretaker(Memento*mo):mo(mo){}
		Memento*getMemento(){return mo;}
		~ Caretaker(){delete mo; mo=NULL;}
	private:
		Memento*mo;
	};

	int main()
	{
		Originator*or1=new Originator();
		or1->add();or1->add();
		Caretaker*cr=new Caretaker(or1->createMO());
		or1->add();or1->add();
		or1->set(cr->getMemento());
		or1->add();
		or1->set(cr->getMemento());
		or1->add();
		delete or1;delete cr;
		return 0;
	}
	[/sourcecode]

<h2>Observer</h2>
	Defines a link between objects so that when one object's state changes, all dependent objects are updated automatically.

	It allows you to monitor and publish changes of a single object called subject.

	When a change occurs other objects called observers can be automatically notified by calling one of their methods.

	Let me give an example, for excel, when you change the content of the grid, the bar chart will change automotify. How to implement it? That can be called <span style="color:red">publish-subscribe</span> pattern.

	<span style="color:red">与前面的差异不大就不写了.</span>

<h2>State</h2>
	It allows an object to completely change its behavior depending upon its current internal state.

	By substituting classes within a defined context, the state object appears to change its type at run-time.

	Two examples. TCPState and DVDState. Change State, the behavior will change.

	Use the State pattern in either of the following cases:
	<ul>
		<li>Behavior depends on its state</li>
		<li>Operations have large, multipart conditional statements that depend on the
			object's state.
		</li>
	</ul>
	[sourcecode language="c"]
	//Memory Leak
	#include <iostream>

	class StateBase;

	class Context{
	public:
		Context(StateBase*sb):_sb(sb){}
		void Request();
		void setState(StateBase*sb){_sb=sb;}
	private:
		StateBase*_sb;
	};

	class StateBase{
	public:
		virtual void Handler(Context*ctx)=0;
	};

	class SC:public StateBase{
	public:
		virtual void Handler(Context*ctx);
	};

	class SB:public StateBase{
	public:
		virtual void Handler(Context*ctx);
	};

	class SA:public StateBase{
	public:
		virtual void Handler(Context*ctx);
	};

	void Context::Request()
	{
		_sb->Handler(this);
	}

	void SA::Handler(Context*ctx)
	{
		std::cout<<"SA Handler"<<std::endl;
		ctx->setState(new SB());
	}

	void SB::Handler(Context*ctx)
	{
		std::cout<<"SB Handler"<<std::endl;
		ctx->setState(new SC());
	}

	void SC::Handler(Context*ctx)
	{
		std::cout<<"SC Handler"<<std::endl;
		ctx->setState(new SA());
	}

	int main()
	{
		Context*ctx=new Context(new SA());
		ctx->Request();
		ctx->Request();
		ctx->Request();
		ctx->Request();

		delete ctx;
		return 0;
	}
	[/sourcecode]

<h2>Strategy</h2>
	It allows a set of similar algorithms to be defined and encapsulated in their own classes.

	The algorithm to be used for a particular purpose may then be selected at run-time according to your requirements.

	<span style="color:red">A very simple pattern.</span>

	[sourcecode language="c"]
	#include <iostream>

	class StrategyBase{
	public:
		virtual void call()=0;
	};

	class Client{
	public:
		void setStrategy(StrategyBase*sb){_sb=sb;}
		void call(){_sb->call();}
	private:
		StrategyBase*_sb;
	};

	class CSA:public StrategyBase{
	public:
		virtual void call()
		{
			std::cout<<"CSA called"<<std::endl;
		}
	};

	class CSB:public StrategyBase{
	public:
		virtual void call()
		{
			std::cout<<"CSB called"<<std::endl;
		}
	};

	class CSC:public StrategyBase{
	public:
		virtual void call()
		{
			std::cout<<"CSC called"<<std::endl;
		}
	};

	int main()
	{
		Client*cl=new Client();
		cl->setStrategy(new CSA());
		cl->call();
		cl->setStrategy(new CSB());
		cl->call();
		cl->setStrategy(new CSC());
		cl->call();
		return 0;
	}
	[/sourcecode]

<h2>Template</h2>
	It allows a group of interchangeable, similarly structured, multi-step algorithms to be defined.

	Each algorithm follows the same series of actions but provides a different implementation of the steps.
	[sourcecode language="c"]
	#include <iostream>

	class AlgorithmBase{
	public:
		virtual void excute()
		{
			step1();
			step2();
		}
		virtual void step1()=0;
		virtual void step2()=0;
	};

	class ConcreteAlgorithmA:public AlgorithmBase{
	public:
		virtual void step1()
		{
			std::cout<<"ConcreteAlgorithmA step1"<<std::endl;
		}
		virtual void step2()
		{
			std::cout<<"ConcreteAlgorithmA step2"<<std::endl;
		}
	};

	class ConcreteAlgorithmB:public AlgorithmBase{
	public:
		virtual void step1()
		{
			std::cout<<"ConcreteAlgorithmB step1"<<std::endl;
		}
		virtual void step2()
		{
			std::cout<<"ConcreteAlgorithmB step2"<<std::endl;
		}
	};

	int main()
	{
		AlgorithmBase*ab=new ConcreteAlgorithmA();
		ab->excute();
		delete ab;ab=NULL;
		ab=new ConcreteAlgorithmB();
		ab->excute();
		delete ab;ab=NULL;
		return 0;
	}
	[/sourcecode]

<h2>Visitor</h2>
	The last pattern in this blog.

	That separates a set of structured data from the functionality that may be performed upon it.

	This promotes loose coupling and enables additional operations to be added without modifying the data classes. Another benefit is the ability to add a new visitor without modifying the existing structure.

	<ul>
		<li>Client</li>
		<li>ObjectStructure</li>
		<li>ElementBase, ConcreteElement</li>
		<li>VisitorBase, ConcreteVisitor</li>
	</ul>

	Use the Visitor pattern when,
	<ul>
		<li>an object structure contains many classes of objects with different interfaces, and you want to perform operations on these objects that depend on their concrete classes.</li>
		<li>many distinct and unrelated operations need to be performed on objects in an object structure.</li>
		<li>the classes defining the object structure rarely change, but you often want to define new operations over the structure.</li>
	</ul>

	<span style="color:red">这个部分比较的难，最后一个难点一定要攻克.</span>
	[sourcecode language="c"]
	#include <iostream>
	#include <vector>

	class ElementBase;

	class VisitorBase{
	public:
		virtual void visit(ElementBase*eb)=0;
	};

	class ElementBase{
	public:
		virtual void visit(VisitorBase*cv)
		{
			cv->visit(this);
		}
		virtual std::string getName()=0;
	};


	class ObjectStructure{
	public:
		virtual void add(ElementBase*eb)
		{
			vElements.push_back(eb);
		}

		virtual void visit(VisitorBase*cv)
		{
			for(int i=0;i<vElements.size();i++)
				vElements[i]->visit(cv);
		}
	private:
		std::vector<ElementBase*> vElements;
	};

	class CEA:public ElementBase{
	public:
		virtual std::string getName()
		{
			return "CEA";
		}
	};

	class CEB:public ElementBase{
	public:
		virtual std::string getName()
		{
			return "CEB";
		}
	};


	class ConcreteVisitor:public VisitorBase{
	public:
		virtual void visit(ElementBase*eb)
		{
			std::cout<<eb->getName()<<std::endl;
		}
	};

	int main()
	{
		ObjectStructure*obs=new ObjectStructure();
		obs->add(new CEA());
		obs->add(new CEA());
		obs->add(new CEB());
		obs->add(new CEB());
		obs->visit(new ConcreteVisitor());
		return 0;
	}
	[/sourcecode]
</body>