C++ 编程/代码/设计模式/行为模式
责任链模式的意图是通过让多个对象有机会处理请求，避免将请求的发送者与接收者耦合。将接收对象链接起来，并将请求沿着链传递，直到某个对象处理它。
#include <iostream>
using namespace std;
class Handler {
protected:
Handler *next;
public:
Handler() {
next = NULL;
}
virtual ~Handler() { }
virtual void request(int value) = 0;
void setNextHandler(Handler *nextInLine) {
next = nextInLine;
}
};
class SpecialHandler : public Handler {
private:
int myLimit;
int myId;
public:
SpecialHandler(int limit, int id) {
myLimit = limit;
myId = id;
}
~SpecialHandler() { }
void request(int value) {
if(value < myLimit) {
cout << "Handler " << myId << " handled the request with a limit of " << myLimit << endl;
} else if(next != NULL) {
next->request(value);
} else {
cout << "Sorry, I am the last handler (" << myId << ") and I can't handle the request." << endl;
}
}
};
int main () {
Handler *h1 = new SpecialHandler(10, 1);
Handler *h2 = new SpecialHandler(20, 2);
Handler *h3 = new SpecialHandler(30, 3);
h1->setNextHandler(h2);
h2->setNextHandler(h3);
h1->request(18);
h1->request(40);
delete h1;
delete h2;
delete h3;
return 0;
}
命令模式是一种对象行为模式，通过将请求封装为对象，来解耦发送者和接收者，从而使您可以用不同的请求参数化客户端，排队或记录请求，以及支持可撤销的操作。它也可以被认为是回调方法的面向对象等价物。
回调：它是注册的函数，根据用户操作在稍后时间点被调用。
#include <iostream>
using namespace std;
/*the Command interface*/
class Command
{
public:
virtual void execute()=0;
};
/*Receiver class*/
class Light {
public:
Light() { }
void turnOn()
{
cout << "The light is on" << endl;
}
void turnOff()
{
cout << "The light is off" << endl;
}
};
/*the Command for turning on the light*/
class FlipUpCommand: public Command
{
public:
FlipUpCommand(Light& light):theLight(light)
{
}
virtual void execute()
{
theLight.turnOn();
}
private:
Light& theLight;
};
/*the Command for turning off the light*/
class FlipDownCommand: public Command
{
public:
FlipDownCommand(Light& light) :theLight(light)
{
}
virtual void execute()
{
theLight.turnOff();
}
private:
Light& theLight;
};
class Switch {
public:
Switch(Command& flipUpCmd, Command& flipDownCmd)
:flipUpCommand(flipUpCmd),flipDownCommand(flipDownCmd)
{
}
void flipUp()
{
flipUpCommand.execute();
}
void flipDown()
{
flipDownCommand.execute();
}
private:
Command& flipUpCommand;
Command& flipDownCommand;
};
/*The test class or client*/
int main()
{
Light lamp;
FlipUpCommand switchUp(lamp);
FlipDownCommand switchDown(lamp);
Switch s(switchUp, switchDown);
s.flipUp();
s.flipDown();
}
给定一种语言，定义其语法的表示以及使用该表示来解释该语言中的语句的解释器。
#include <iostream>
#include <string>
#include <map>
#include <list>
namespace wikibooks_design_patterns
{
// based on the Java sample around here
typedef std::string String;
struct Expression;
typedef std::map<String,Expression*> Map;
typedef std::list<Expression*> Stack;
struct Expression {
virtual int interpret(Map variables) = 0;
virtual ~Expression() {}
};
class Number : public Expression {
private:
int number;
public:
Number(int number) { this->number = number; }
int interpret(Map variables) { return number; }
};
class Plus : public Expression {
Expression* leftOperand;
Expression* rightOperand;
public:
Plus(Expression* left, Expression* right) {
leftOperand = left;
rightOperand = right;
}
~Plus(){
delete leftOperand;
delete rightOperand;
}
int interpret(Map variables) {
return leftOperand->interpret(variables) + rightOperand->interpret(variables);
}
};
class Minus : public Expression {
Expression* leftOperand;
Expression* rightOperand;
public:
Minus(Expression* left, Expression* right) {
leftOperand = left;
rightOperand = right;
}
~Minus(){
delete leftOperand;
delete rightOperand;
}
int interpret(Map variables) {
return leftOperand->interpret(variables) - rightOperand->interpret(variables);
}
};
class Variable : public Expression {
String name;
public:
Variable(String name) { this->name = name; }
int interpret(Map variables) {
if(variables.end() == variables.find(name)) return 0;
return variables[name]->interpret(variables);
}
};
// While the interpreter pattern does not address parsing, a parser is provided for completeness.
class Evaluator : public Expression {
Expression* syntaxTree;
public:
Evaluator(String expression){
Stack expressionStack;
size_t last = 0;
for (size_t next = 0; String::npos != last; last = (String::npos == next) ? next : (1+next)) {
next = expression.find(' ', last);
String token( expression.substr(last, (String::npos == next) ? (expression.length()-last) : (next-last)));
if (token == "+") {
Expression* right = expressionStack.back(); expressionStack.pop_back();
Expression* left = expressionStack.back(); expressionStack.pop_back();
Expression* subExpression = new Plus(right, left);
expressionStack.push_back( subExpression );
}
else if (token == "-") {
// it's necessary remove first the right operand from the stack
Expression* right = expressionStack.back(); expressionStack.pop_back();
// ..and after the left one
Expression* left = expressionStack.back(); expressionStack.pop_back();
Expression* subExpression = new Minus(left, right);
expressionStack.push_back( subExpression );
}
else
expressionStack.push_back( new Variable(token) );
}
syntaxTree = expressionStack.back(); expressionStack.pop_back();
}
~Evaluator() {
delete syntaxTree;
}
int interpret(Map context) {
return syntaxTree->interpret(context);
}
};
}
void main()
{
using namespace wikibooks_design_patterns;
Evaluator sentence("w x z - +");
static
const int sequences[][3] = {
{5, 10, 42}, {1, 3, 2}, {7, 9, -5},
};
for (size_t i = 0; sizeof(sequences)/sizeof(sequences[0]) > i; ++i) {
Map variables;
variables["w"] = new Number(sequences[i][0]);
variables["x"] = new Number(sequences[i][1]);
variables["z"] = new Number(sequences[i][2]);
int result = sentence.interpret(variables);
for (Map::iterator it = variables.begin(); variables.end() != it; ++it) delete it->second;
std::cout<<"Interpreter result: "<<result<<std::endl;
}
}
“迭代器”设计模式在 STL 中被广泛用于遍历各种容器。完全理解这一点将使开发人员能够创建高度可重用且易于理解的[需要引用] 数据容器。
迭代器的基本思想是它允许遍历容器（就像指针在数组中移动一样）。但是，要获取容器的下一个元素，您不需要知道容器是如何构造的。这是迭代器的作用。通过简单地使用迭代器提供的成员函数，您可以按照容器的预期顺序从第一个元素移动到最后一个元素。
让我们从考虑一个传统的单维数组开始，指针从起点移动到终点。此示例假定您了解指针运算。请注意，从此以后，“it”或“itr”是“迭代器”的缩写。
const int ARRAY_LEN = 42;
int *myArray = new int[ARRAY_LEN];
// Set the iterator to point to the first memory location of the array
int *arrayItr = myArray;
// Move through each element of the array, setting it equal to its position in the array
for(int i = 0; i < ARRAY_LEN; ++i)
{
// set the value of the current location in the array
*arrayItr = i;
// by incrementing the pointer, we move it to the next position in the array.
// This is easy for a contiguous memory container, since pointer arithmetic
// handles the traversal.
++arrayItr;
}
// Do not be messy, clean up after yourself
delete[] myArray;
这段代码对于数组来说非常快，但是如果内存不连续，我们如何遍历链表呢？考虑以下基本链表的实现
class IteratorCannotMoveToNext{}; // Error class
class MyIntLList
{
public:
// The Node class represents a single element in the linked list.
// The node has a next node and a previous node, so that the user
// may move from one position to the next, or step back a single
// position. Notice that the traversal of a linked list is O(N),
// as is searching, since the list is not ordered.
class Node
{
public:
Node():mNextNode(0),mPrevNode(0),mValue(0){}
Node *mNextNode;
Node *mPrevNode;
int mValue;
};
MyIntLList():mSize(0)
{}
~MyIntLList()
{
while(!Empty())
pop_front();
} // See expansion for further implementation;
int Size() const {return mSize;}
// Add this value to the end of the list
void push_back(int value)
{
Node *newNode = new Node;
newNode->mValue = value;
newNode->mPrevNode = mTail;
mTail->mNextNode = newNode;
mTail = newNode;
++mSize;
}
// Remove the value from the beginning of the list
void pop_front()
{
if(Empty())
return;
Node *tmpnode = mHead;
mHead = mHead->mNextNode;
delete tmpnode;
--mSize;
}
bool Empty()
{return mSize == 0;}
// This is where the iterator definition will go,
// but lets finish the definition of the list, first
private:
Node *mHead;
Node *mTail;
int mSize;
};
这个链表的内存不连续，因此不适合指针运算。我们也不想将链表的内部暴露给其他开发人员，迫使他们学习它，并阻止我们更改它。
这就是迭代器发挥作用的地方。通用接口使学习容器的用法更容易，并将遍历逻辑隐藏在其他开发人员面前。
让我们检查一下迭代器本身的代码。
/*
* The iterator class knows the internals of the linked list, so that it
* may move from one element to the next. In this implementation, I have
* chosen the classic traversal method of overloading the increment
* operators. More thorough implementations of a bi-directional linked
* list would include decrement operators so that the iterator may move
* in the opposite direction.
*/
class Iterator
{
public:
Iterator(Node *position):mCurrNode(position){}
// Prefix increment
const Iterator &operator++()
{
if(mCurrNode == 0 || mCurrNode->mNextNode == 0)
throw IteratorCannotMoveToNext();e
mCurrNode = mCurrNode->mNextNode;
return *this;
}
// Postfix increment
Iterator operator++(int)
{
Iterator tempItr = *this;
++(*this);
return tempItr;
}
// Dereferencing operator returns the current node, which should then
// be dereferenced for the int. TODO: Check syntax for overloading
// dereferencing operator
Node * operator*()
{return mCurrNode;}
// TODO: implement arrow operator and clean up example usage following
private:
Node *mCurrNode;
};
// The following two functions make it possible to create
// iterators for an instance of this class.
// First position for iterators should be the first element in the container.
Iterator Begin(){return Iterator(mHead);}
// Final position for iterators should be one past the last element in the container.
Iterator End(){return Iterator(0);}
通过这种实现，现在可以不了解容器的大小或其数据是如何组织的，就可以按顺序遍历每个元素，操作或简单地访问数据。这是通过 MyIntLList 类中的访问器 Begin() 和 End() 来完成的。
// Create a list
MyIntLList myList;
// Add some items to the list
for(int i = 0; i < 10; ++i)
myList.push_back(i);
// Move through the list, adding 42 to each item.
for(MyIntLList::Iterator it = myList.Begin(); it != myList.End(); ++it)
(*it)->mValue += 42;
以下程序给出了使用泛型模板的迭代器设计模式的实现
/************************************************************************/
/* Iterator.h */
/************************************************************************/
#ifndef MY_ITERATOR_HEADER
#define MY_ITERATOR_HEADER
#include <iterator>
#include <vector>
#include <set>
//////////////////////////////////////////////////////////////////////////
template<class T, class U>
class Iterator
{
public:
typedef typename std::vector<T>::iterator iter_type;
Iterator(U *pData):m_pData(pData){
m_it = m_pData->m_data.begin();
}
void first()
{
m_it = m_pData->m_data.begin();
}
void next()
{
m_it++;
}
bool isDone()
{
return (m_it == m_pData->m_data.end());
}
iter_type current()
{
return m_it;
}
private:
U *m_pData;
iter_type m_it;
};
template<class T, class U, class A>
class setIterator
{
public:
typedef typename std::set<T,U>::iterator iter_type;
setIterator(A *pData):m_pData(pData)
{
m_it = m_pData->m_data.begin();
}
void first()
{
m_it = m_pData->m_data.begin();
}
void next()
{
m_it++;
}
bool isDone()
{
return (m_it == m_pData->m_data.end());
}
iter_type current()
{
return m_it;
}
private:
A *m_pData;
iter_type m_it;
};
#endif
/************************************************************************/
/* Aggregate.h */
/************************************************************************/
#ifndef MY_DATACOLLECTION_HEADER
#define MY_DATACOLLECTION_HEADER
#include "Iterator.h"
template <class T>
class aggregate
{
friend class Iterator<T, aggregate>;
public:
void add(T a)
{
m_data.push_back(a);
}
Iterator<T, aggregate> *create_iterator()
{
return new Iterator<T, aggregate>(this);
}
private:
std::vector<T> m_data;
};
template <class T, class U>
class aggregateSet
{
friend class setIterator<T, U, aggregateSet>;
public:
void add(T a)
{
m_data.insert(a);
}
setIterator<T, U, aggregateSet> *create_iterator()
{
return new setIterator<T,U,aggregateSet>(this);
}
void Print()
{
copy(m_data.begin(), m_data.end(), std::ostream_iterator<T>(std::cout, "\n"));
}
private:
std::set<T,U> m_data;
};
#endif
/************************************************************************/
/* Iterator Test.cpp */
/************************************************************************/
#include <iostream>
#include <string>
#include "Aggregate.h"
using namespace std;
class Money
{
public:
Money(int a = 0): m_data(a) {}
void SetMoney(int a)
{
m_data = a;
}
int GetMoney()
{
return m_data;
}
private:
int m_data;
};
class Name
{
public:
Name(string name): m_name(name) {}
const string &GetName() const
{
return m_name;
}
friend ostream &operator<<(ostream& out, Name name)
{
out << name.GetName();
return out;
}
private:
string m_name;
};
struct NameLess
{
bool operator()(const Name &lhs, const Name &rhs) const
{
return (lhs.GetName() < rhs.GetName());
}
};
int main()
{
//sample 1
cout << "________________Iterator with int______________________________________" << endl;
aggregate<int> agg;
for (int i = 0; i < 10; i++)
agg.add(i);
Iterator< int,aggregate<int> > *it = agg.create_iterator();
for(it->first(); !it->isDone(); it->next())
cout << *it->current() << endl;
//sample 2
aggregate<Money> agg2;
Money a(100), b(1000), c(10000);
agg2.add(a);
agg2.add(b);
agg2.add(c);
cout << "________________Iterator with Class Money______________________________" << endl;
Iterator<Money, aggregate<Money> > *it2 = agg2.create_iterator();
for (it2->first(); !it2->isDone(); it2->next())
cout << it2->current()->GetMoney() << endl;
//sample 3
cout << "________________Set Iterator with Class Name______________________________" << endl;
aggregateSet<Name, NameLess> aset;
aset.add(Name("Qmt"));
aset.add(Name("Bmt"));
aset.add(Name("Cmt"));
aset.add(Name("Amt"));
setIterator<Name, NameLess, aggregateSet<Name, NameLess> > *it3 = aset.create_iterator();
for (it3->first(); !it3->isDone(); it3->next())
cout << (*it3->current()) << endl;
}
控制台输出
________________Iterator with int______________________________________ 0 1 2 3 4 5 6 7 8 9 ________________Iterator with Class Money______________________________ 100 1000 10000 ________________Set Iterator with Class Name___________________________ Amt Bmt Cmt Qmt
定义一个对象来封装一组对象如何交互。中介者通过防止对象显式地相互引用来促进松散耦合，并且它允许您独立地改变它们的交互。
#include <iostream>
#include <string>
#include <list>
class MediatorInterface;
class ColleagueInterface {
std::string name;
public:
ColleagueInterface (const std::string& newName) : name (newName) {}
std::string getName() const {return name;}
virtual void sendMessage (const MediatorInterface&, const std::string&) const = 0;
virtual void receiveMessage (const ColleagueInterface*, const std::string&) const = 0;
};
class Colleague : public ColleagueInterface {
public:
using ColleagueInterface::ColleagueInterface;
virtual void sendMessage (const MediatorInterface&, const std::string&) const override;
private:
virtual void receiveMessage (const ColleagueInterface*, const std::string&) const override;
};
class MediatorInterface {
private:
std::list<ColleagueInterface*> colleagueList;
public:
const std::list<ColleagueInterface*>& getColleagueList() const {return colleagueList;}
virtual void distributeMessage (const ColleagueInterface*, const std::string&) const = 0;
virtual void registerColleague (ColleagueInterface* colleague) {colleagueList.emplace_back (colleague);}
};
class Mediator : public MediatorInterface {
virtual void distributeMessage (const ColleagueInterface*, const std::string&) const override;
};
void Colleague::sendMessage (const MediatorInterface& mediator, const std::string& message) const {
mediator.distributeMessage (this, message);
}
void Colleague::receiveMessage (const ColleagueInterface* sender, const std::string& message) const {
std::cout << getName() << " received the message from " << sender->getName() << ": " << message << std::endl;
}
void Mediator::distributeMessage (const ColleagueInterface* sender, const std::string& message) const {
for (const ColleagueInterface* x : getColleagueList())
if (x != sender) // Do not send the message back to the sender
x->receiveMessage (sender, message);
}
int main() {
Colleague *bob = new Colleague ("Bob"), *sam = new Colleague ("Sam"), *frank = new Colleague ("Frank"), *tom = new Colleague ("Tom");
Colleague* staff[] = {bob, sam, frank, tom};
Mediator mediatorStaff, mediatorSamsBuddies;
for (Colleague* x : staff)
mediatorStaff.registerColleague(x);
bob->sendMessage (mediatorStaff, "I'm quitting this job!");
mediatorSamsBuddies.registerColleague (frank); mediatorSamsBuddies.registerColleague (tom); // Sam's buddies only
sam->sendMessage (mediatorSamsBuddies, "Hooray! He's gone! Let's go for a drink, guys!");
return 0;
}
备忘录模式不会违反封装，它将捕获和外部化对象的内部状态，以便该对象可以稍后恢复到该状态。虽然 四人帮 使用 friend 作为实现这种模式的一种方式，但它不是最佳设计[需要引用]。它也可以使用 PIMPL（指向实现的指针或不透明指针） 来实现。最佳用例是编辑器中的“撤消-重做”。
发起者（要保存的对象）将自己的快照创建为备忘录对象，并将该引用传递给看护者对象。看护者对象保留备忘录，直到发起者可能希望恢复到备忘录对象中记录的先前状态。
参见 memoize，了解这种模式的旧式示例。
#include <iostream>
#include <string>
#include <sstream>
#include <vector>
const std::string NAME = "Object";
template <typename T>
std::string toString (const T& t) {
std::stringstream ss;
ss << t;
return ss.str();
}
class Memento;
class Object {
private:
int value;
std::string name;
double decimal; // and suppose there are loads of other data members
public:
Object (int newValue): value (newValue), name (NAME + toString (value)), decimal ((float)value / 100) {}
void doubleValue() {value = 2 * value; name = NAME + toString (value); decimal = (float)value / 100;}
void increaseByOne() {value++; name = NAME + toString (value); decimal = (float)value / 100;}
int getValue() const {return value;}
std::string getName() const {return name;}
double getDecimal() const {return decimal;}
Memento* createMemento() const;
void reinstateMemento (Memento* mem);
};
class Memento {
private:
Object object;
public:
Memento (const Object& obj): object (obj) {}
Object snapshot() const {return object;} // want a snapshot of Object itself because of its many data members
};
Memento* Object::createMemento() const {
return new Memento (*this);
}
void Object::reinstateMemento (Memento* mem) {
*this = mem->snapshot();
}
class Command {
private:
typedef void (Object::*Action)();
Object* receiver;
Action action;
static std::vector<Command*> commandList;
static std::vector<Memento*> mementoList;
static int numCommands;
static int maxCommands;
public:
Command (Object *newReceiver, Action newAction): receiver (newReceiver), action (newAction) {}
virtual void execute() {
if (mementoList.size() < numCommands + 1)
mementoList.resize (numCommands + 1);
mementoList[numCommands] = receiver->createMemento(); // saves the last value
if (commandList.size() < numCommands + 1)
commandList.resize (numCommands + 1);
commandList[numCommands] = this; // saves the last command
if (numCommands > maxCommands)
maxCommands = numCommands;
numCommands++;
(receiver->*action)();
}
static void undo() {
if (numCommands == 0)
{
std::cout << "There is nothing to undo at this point." << std::endl;
return;
}
commandList[numCommands - 1]->receiver->reinstateMemento (mementoList[numCommands - 1]);
numCommands--;
}
void static redo() {
if (numCommands > maxCommands)
{
std::cout << "There is nothing to redo at this point." << std::endl;
return ;
}
Command* commandRedo = commandList[numCommands];
(commandRedo->receiver->*(commandRedo->action))();
numCommands++;
}
};
std::vector<Command*> Command::commandList;
std::vector<Memento*> Command::mementoList;
int Command::numCommands = 0;
int Command::maxCommands = 0;
int main()
{
int i;
std::cout << "Please enter an integer: ";
std::cin >> i;
Object *object = new Object(i);
Command *commands[3];
commands[1] = new Command(object, &Object::doubleValue);
commands[2] = new Command(object, &Object::increaseByOne);
std::cout << "0.Exit, 1.Double, 2.Increase by one, 3.Undo, 4.Redo: ";
std::cin >> i;
while (i != 0)
{
if (i == 3)
Command::undo();
else if (i == 4)
Command::redo();
else if (i > 0 && i <= 2)
commands[i]->execute();
else
{
std::cout << "Enter a proper choice: ";
std::cin >> i;
continue;
}
std::cout << " " << object->getValue() << " " << object->getName() << " " << object->getDecimal() << std::endl;
std::cout << "0.Exit, 1.Double, 2.Increase by one, 3.Undo, 4.Redo: ";
std::cin >> i;
}
}
观察者模式定义了对象之间的一对多依赖关系，以便当一个对象改变状态时，所有其依赖项都会被自动通知并更新。
- 问题
- 在应用程序中的一个地方或多个地方，我们需要了解系统事件或应用程序状态更改。我们希望有一个标准的方式来订阅监听系统事件，以及一个标准的方式来通知感兴趣的方。在感兴趣的一方订阅系统事件或应用程序状态更改后，通知应该是自动的。还应该有一种取消订阅的方法。
- 力量
- 观察者和可观察者可能应该由对象表示。观察者对象将由可观察者对象通知。
- 解决方案
- 订阅后，监听对象将通过方法调用方式通知。
#include <list>
#include <algorithm>
#include <iostream>
using namespace std;
// The Abstract Observer
class ObserverBoardInterface
{
public:
virtual void update(float a,float b,float c) = 0;
};
// Abstract Interface for Displays
class DisplayBoardInterface
{
public:
virtual void show() = 0;
};
// The Abstract Subject
class WeatherDataInterface
{
public:
virtual void registerOb(ObserverBoardInterface* ob) = 0;
virtual void removeOb(ObserverBoardInterface* ob) = 0;
virtual void notifyOb() = 0;
};
// The Concrete Subject
class ParaWeatherData: public WeatherDataInterface
{
public:
void SensorDataChange(float a,float b,float c)
{
m_humidity = a;
m_temperature = b;
m_pressure = c;
notifyOb();
}
void registerOb(ObserverBoardInterface* ob)
{
m_obs.push_back(ob);
}
void removeOb(ObserverBoardInterface* ob)
{
m_obs.remove(ob);
}
protected:
void notifyOb()
{
list<ObserverBoardInterface*>::iterator pos = m_obs.begin();
while (pos != m_obs.end())
{
((ObserverBoardInterface* )(*pos))->update(m_humidity,m_temperature,m_pressure);
(dynamic_cast<DisplayBoardInterface*>(*pos))->show();
++pos;
}
}
private:
float m_humidity;
float m_temperature;
float m_pressure;
list<ObserverBoardInterface* > m_obs;
};
// A Concrete Observer
class CurrentConditionBoard : public ObserverBoardInterface, public DisplayBoardInterface
{
public:
CurrentConditionBoard(ParaWeatherData& a):m_data(a)
{
m_data.registerOb(this);
}
void show()
{
cout<<"_____CurrentConditionBoard_____"<<endl;
cout<<"humidity: "<<m_h<<endl;
cout<<"temperature: "<<m_t<<endl;
cout<<"pressure: "<<m_p<<endl;
cout<<"_______________________________"<<endl;
}
void update(float h, float t, float p)
{
m_h = h;
m_t = t;
m_p = p;
}
private:
float m_h;
float m_t;
float m_p;
ParaWeatherData& m_data;
};
// A Concrete Observer
class StatisticBoard : public ObserverBoardInterface, public DisplayBoardInterface
{
public:
StatisticBoard(ParaWeatherData& a):m_maxt(-1000),m_mint(1000),m_avet(0),m_count(0),m_data(a)
{
m_data.registerOb(this);
}
void show()
{
cout<<"________StatisticBoard_________"<<endl;
cout<<"lowest temperature: "<<m_mint<<endl;
cout<<"highest temperature: "<<m_maxt<<endl;
cout<<"average temperature: "<<m_avet<<endl;
cout<<"_______________________________"<<endl;
}
void update(float h, float t, float p)
{
++m_count;
if (t>m_maxt)
{
m_maxt = t;
}
if (t<m_mint)
{
m_mint = t;
}
m_avet = (m_avet * (m_count-1) + t)/m_count;
}
private:
float m_maxt;
float m_mint;
float m_avet;
int m_count;
ParaWeatherData& m_data;
};
int main(int argc, char *argv[])
{
ParaWeatherData * wdata = new ParaWeatherData;
CurrentConditionBoard* currentB = new CurrentConditionBoard(*wdata);
StatisticBoard* statisticB = new StatisticBoard(*wdata);
wdata->SensorDataChange(10.2, 28.2, 1001);
wdata->SensorDataChange(12, 30.12, 1003);
wdata->SensorDataChange(10.2, 26, 806);
wdata->SensorDataChange(10.3, 35.9, 900);
wdata->removeOb(currentB);
wdata->SensorDataChange(100, 40, 1900);
delete statisticB;
delete currentB;
delete wdata;
return 0;
}
状态模式允许对象在内部状态发生改变时改变其行为。该对象将看起来像是改变了它的类。
#include <iostream>
#include <string>
#include <cstdlib>
#include <ctime>
#include <memory>
enum Input {DUCK_DOWN, STAND_UP, JUMP, DIVE};
class Fighter;
class StandingState; class JumpingState; class DivingState;
class FighterState {
public:
static std::shared_ptr<StandingState> standing;
static std::shared_ptr<DivingState> diving;
virtual ~FighterState() = default;
virtual void handleInput (Fighter&, Input) = 0;
virtual void update (Fighter&) = 0;
};
class DuckingState : public FighterState {
private:
int chargingTime;
static const int FullRestTime = 5;
public:
DuckingState() : chargingTime(0) {}
virtual void handleInput (Fighter&, Input) override;
virtual void update (Fighter&) override;
};
class StandingState : public FighterState {
public:
virtual void handleInput (Fighter&, Input) override;
virtual void update (Fighter&) override;
};
class JumpingState : public FighterState {
private:
int jumpingHeight;
public:
JumpingState() {jumpingHeight = std::rand() % 5 + 1;}
virtual void handleInput (Fighter&, Input) override;
virtual void update (Fighter&) override;
};
class DivingState : public FighterState {
public:
virtual void handleInput (Fighter&, Input) override;
virtual void update (Fighter&) override;
};
std::shared_ptr<StandingState> FighterState::standing (new StandingState);
std::shared_ptr<DivingState> FighterState::diving (new DivingState);
class Fighter {
private:
std::string name;
std::shared_ptr<FighterState> state;
int fatigueLevel = std::rand() % 10;
public:
Fighter (const std::string& newName) : name (newName), state (FighterState::standing) {}
std::string getName() const {return name;}
int getFatigueLevel() const {return fatigueLevel;}
virtual void handleInput (Input input) {state->handleInput (*this, input);} // delegate input handling to 'state'.
void changeState (std::shared_ptr<FighterState> newState) {state = newState; updateWithNewState();}
void standsUp() {std::cout << getName() << " stands up." << std::endl;}
void ducksDown() {std::cout << getName() << " ducks down." << std::endl;}
void jumps() {std::cout << getName() << " jumps into the air." << std::endl;}
void dives() {std::cout << getName() << " makes a dive attack in the middle of the jump!" << std::endl;}
void feelsStrong() {std::cout << getName() << " feels strong!" << std::endl;}
void changeFatigueLevelBy (int change) {fatigueLevel += change; std::cout << "fatigueLevel = " << fatigueLevel << std::endl;}
private:
virtual void updateWithNewState() {state->update(*this);} // delegate updating to 'state'
};
void StandingState::handleInput (Fighter& fighter, Input input) {
switch (input) {
case STAND_UP: std::cout << fighter.getName() << " remains standing." << std::endl; return;
case DUCK_DOWN: fighter.changeState (std::shared_ptr<DuckingState> (new DuckingState)); return fighter.ducksDown();
case JUMP: fighter.jumps(); return fighter.changeState (std::shared_ptr<JumpingState> (new JumpingState));
default: std::cout << "One cannot do that while standing. " << fighter.getName() << " remains standing by default." << std::endl;
}
}
void StandingState::update (Fighter& fighter) {
if (fighter.getFatigueLevel() > 0)
fighter.changeFatigueLevelBy(-1);
}
void DuckingState::handleInput (Fighter& fighter, Input input) {
switch (input) {
case STAND_UP: fighter.changeState (FighterState::standing); return fighter.standsUp();
case DUCK_DOWN:
std::cout << fighter.getName() << " remains in ducking position, ";
if (chargingTime < FullRestTime) std::cout << "recovering in the meantime." << std::endl;
else std::cout << "fully recovered." << std::endl;
return update (fighter);
default:
std::cout << "One cannot do that while ducking. " << fighter.getName() << " remains in ducking position by default." << std::endl;
update (fighter);
}
}
void DuckingState::update (Fighter& fighter) {
chargingTime++;
std::cout << "Charging time = " << chargingTime << "." << std::endl;
if (fighter.getFatigueLevel() > 0)
fighter.changeFatigueLevelBy(-1);
if (chargingTime >= FullRestTime && fighter.getFatigueLevel() <= 3)
fighter.feelsStrong();
}
void JumpingState::handleInput (Fighter& fighter, Input input) {
switch (input) {
case DIVE: fighter.changeState (FighterState::diving); return fighter.dives();
default:
std::cout << "One cannot do that in the middle of a jump. " << fighter.getName() << " lands from his jump and is now standing again." << std::endl;
fighter.changeState (FighterState::standing);
}
}
void JumpingState::update (Fighter& fighter) {
std::cout << fighter.getName() << " has jumped " << jumpingHeight << " feet into the air." << std::endl;
if (jumpingHeight >= 3)
fighter.changeFatigueLevelBy(1);
}
void DivingState::handleInput (Fighter& fighter, Input) {
std::cout << "Regardless of what the user input is, " << fighter.getName() << " lands from his dive and is now standing again." << std::endl;
fighter.changeState (FighterState::standing);
}
void DivingState::update (Fighter& fighter) {
fighter.changeFatigueLevelBy(2);
}
int main() {
std::srand(std::time(nullptr));
Fighter rex ("Rex the Fighter"), borg ("Borg the Fighter");
std::cout << rex.getName() << " and " << borg.getName() << " are currently standing." << std::endl;
int choice;
auto chooseAction = [&choice](Fighter& fighter) {
std::cout << std::endl << DUCK_DOWN + 1 << ") Duck down " << STAND_UP + 1 << ") Stand up " << JUMP + 1
<< ") Jump " << DIVE + 1 << ") Dive in the middle of a jump" << std::endl;
std::cout << "Choice for " << fighter.getName() << "? ";
std::cin >> choice;
const Input input1 = static_cast<Input>(choice - 1);
fighter.handleInput (input1);
};
while (true) {
chooseAction (rex);
chooseAction (borg);
}
}
定义一系列算法，封装每个算法，并使它们可互换。策略允许算法独立于使用它的客户端而变化。
#include <iostream>
using namespace std;
class StrategyInterface
{
public:
virtual void execute() const = 0;
};
class ConcreteStrategyA: public StrategyInterface
{
public:
void execute() const override
{
cout << "Called ConcreteStrategyA execute method" << endl;
}
};
class ConcreteStrategyB: public StrategyInterface
{
public:
void execute() const override
{
cout << "Called ConcreteStrategyB execute method" << endl;
}
};
class ConcreteStrategyC: public StrategyInterface
{
public:
void execute() const override
{
cout << "Called ConcreteStrategyC execute method" << endl;
}
};
class Context
{
private:
StrategyInterface * strategy_;
public:
explicit Context(StrategyInterface *strategy):strategy_(strategy)
{
}
void set_strategy(StrategyInterface *strategy)
{
strategy_ = strategy;
}
void execute() const
{
strategy_->execute();
}
};
int main(int argc, char *argv[])
{
ConcreteStrategyA concreteStrategyA;
ConcreteStrategyB concreteStrategyB;
ConcreteStrategyC concreteStrategyC;
Context contextA(&concreteStrategyA);
Context contextB(&concreteStrategyB);
Context contextC(&concreteStrategyC);
contextA.execute(); // output: "Called ConcreteStrategyA execute method"
contextB.execute(); // output: "Called ConcreteStrategyB execute method"
contextC.execute(); // output: "Called ConcreteStrategyC execute method"
contextA.set_strategy(&concreteStrategyB);
contextA.execute(); // output: "Called ConcreteStrategyB execute method"
contextA.set_strategy(&concreteStrategyC);
contextA.execute(); // output: "Called ConcreteStrategyC execute method"
return 0;
}
通过在一个操作中定义算法的骨架，将某些步骤推迟到子类，模板方法允许子类重新定义该算法的某些步骤，而不会改变算法的结构。
#include <ctime>
#include <assert.h>
#include <iostream>
namespace wikibooks_design_patterns
{
/**
* An abstract class that is common to several games in
* which players play against the others, but only one is
* playing at a given time.
*/
class Game
{
public:
Game(): playersCount(0), movesCount(0), playerWon(-1)
{
srand( (unsigned)time( NULL));
}
/* A template method : */
void playOneGame(const int playersCount = 0)
{
if (playersCount)
{
this->playersCount = playersCount;
}
InitializeGame();
assert(this->playersCount);
int j = 0;
while (!endOfGame())
{
makePlay(j);
j = (j + 1) % this->playersCount;
if (!j)
{
++movesCount;
}
}
printWinner();
}
protected:
virtual void initializeGame() = 0;
virtual void makePlay(int player) = 0;
virtual bool endOfGame() = 0;
virtual void printWinner() = 0;
private:
void InitializeGame()
{
movesCount = 0;
playerWon = -1;
initializeGame();
}
protected:
int playersCount;
int movesCount;
int playerWon;
};
//Now we can extend this class in order
//to implement actual games:
class Monopoly: public Game {
/* Implementation of necessary concrete methods */
void initializeGame() {
// Initialize players
playersCount = rand() * 7 / RAND_MAX + 2;
// Initialize money
}
void makePlay(int player) {
// Process one turn of player
// Decide winner
if (movesCount < 20)
return;
const int chances = (movesCount > 199) ? 199 : movesCount;
const int random = MOVES_WIN_CORRECTION * rand() * 200 / RAND_MAX;
if (random < chances)
playerWon = player;
}
bool endOfGame() {
// Return true if game is over
// according to Monopoly rules
return (-1 != playerWon);
}
void printWinner() {
assert(playerWon >= 0);
assert(playerWon < playersCount);
// Display who won
std::cout<<"Monopoly, player "<<playerWon<<" won in "<<movesCount<<" moves."<<std::endl;
}
private:
enum
{
MOVES_WIN_CORRECTION = 20,
};
};
class Chess: public Game {
/* Implementation of necessary concrete methods */
void initializeGame() {
// Initialize players
playersCount = 2;
// Put the pieces on the board
}
void makePlay(int player) {
assert(player < playersCount);
// Process a turn for the player
// decide winner
if (movesCount < 2)
return;
const int chances = (movesCount > 99) ? 99 : movesCount;
const int random = MOVES_WIN_CORRECTION * rand() * 100 / RAND_MAX;
//std::cout<<random<<" : "<<chances<<std::endl;
if (random < chances)
playerWon = player;
}
bool endOfGame() {
// Return true if in Checkmate or
// Stalemate has been reached
return (-1 != playerWon);
}
void printWinner() {
assert(playerWon >= 0);
assert(playerWon < playersCount);
// Display the winning player
std::cout<<"Player "<<playerWon<<" won in "<<movesCount<<" moves."<<std::endl;
}
private:
enum
{
MOVES_WIN_CORRECTION = 7,
};
};
}
int main()
{
using namespace wikibooks_design_patterns;
Game* game = NULL;
Chess chess;
game = &chess;
for (unsigned i = 0; i < 100; ++i)
game->playOneGame();
Monopoly monopoly;
game = &monopoly;
for (unsigned i = 0; i < 100; ++i)
game->playOneGame();
return 0;
}
访问者模式将代表一个操作，该操作将在对象结构的元素上执行，通过允许您定义新的操作，而无需更改其操作的元素类。
#include <string>
#include <iostream>
#include <vector>
#include <memory>
using namespace std;
class Wheel;
class Engine;
class Body;
class Car;
// interface to all car 'parts'
struct CarElementVisitor
{
virtual void visit(Wheel& wheel) const = 0;
virtual void visit(Engine& engine) const = 0;
virtual void visit(Body& body) const = 0;
virtual void visitCar(Car& car) const = 0;
};
// interface to one part
struct CarElement
{
virtual void accept(const CarElementVisitor& visitor) = 0;
};
// wheel element, there are four wheels with unique names
class Wheel : public CarElement
{
public:
explicit Wheel(const string& name) : name_(name){}
const string& getName() const
{
return name_;
}
void accept(const CarElementVisitor& visitor)
{
visitor.visit(*this);
}
private:
string name_;
};
class Engine : public CarElement
{
public:
void accept(const CarElementVisitor& visitor)
{
visitor.visit(*this);
}
};
class Body : public CarElement
{
public:
void accept(const CarElementVisitor& visitor)
{
visitor.visit(*this);
}
};
class Car
{
public:
vector<unique_ptr<CarElement>>& getElements()
{
return elements_;
}
Car() {
// assume that neither push_back nor Wheel(const string&) may throw
elements_.push_back( make_unique<Wheel>("front left") );
elements_.push_back( make_unique<Wheel>("front right") );
elements_.push_back( make_unique<Wheel>("back left") );
elements_.push_back( make_unique<Wheel>("back right") );
elements_.push_back( make_unique<Body>() );
elements_.push_back( make_unique<Engine>() );
}
private:
vector<unique_ptr<CarElement>> elements_;
};
// PrintVisitor and DoVisitor show by using a different implementation the Car class is unchanged even though the algorithm is different in PrintVisitor and DoVisitor.
class CarElementPrintVisitor : public CarElementVisitor
{
public:
void visit(Wheel& wheel) const
{
cout << "Visiting " << wheel.getName() << " wheel" << endl;
}
void visit(Engine& engine) const
{
cout << "Visiting engine" << endl;
}
void visit(Body& body) const
{
cout << "Visiting body" << endl;
}
void visitCar(Car& car) const
{
cout << endl << "Visiting car" << endl;
vector<unique_ptr<CarElement>>& elems = car.getElements();
for(auto &it : elems)
{
// this issues the callback i.e. to this from the element
it->accept(*this);
}
cout << "Visited car" << endl;
}
};
class CarElementDoVisitor : public CarElementVisitor
{
public:
// these are specific implementations added to the original object without modifying the original struct
void visit(Wheel& wheel) const
{
cout << "Kicking my " << wheel.getName() << " wheel" << endl;
}
void visit(Engine& engine) const
{
cout << "Starting my engine" << endl;
}
void visit(Body& body) const
{
cout << "Moving my body" << endl;
}
void visitCar(Car& car) const
{
cout << endl << "Starting my car" << endl;
vector<unique_ptr<CarElement>>& elems = car.getElements();
for(auto& it : elems)
{
it->accept(*this); // this issues the callback i.e. to this from the element
}
cout << "Stopped car" << endl;
}
};
int main()
{
Car car;
CarElementPrintVisitor printVisitor;
CarElementDoVisitor doVisitor;
printVisitor.visitCar(car);
doVisitor.visitCar(car);
return 0;
}
一种模式，常用于需要维护相同数据的多个视图的应用程序。模型-视图-控制器模式直到最近[需要引用] 是一个非常常见的模式，尤其是在图形用户界面编程中，它将代码分成 3 部分。模型、视图和控制器。
模型是实际的数据表示（例如，数组与链表）或其他表示数据库的对象。视图是读取模型的界面或胖客户端 GUI。控制器提供了更改或修改数据的界面，然后选择“最佳下一个视图”(NBV)。
新手可能会认为这种“MVC”模型是浪费的，主要是因为您在运行时使用了许多额外的对象，而这看起来像是可以用一个巨大的对象来完成的。但 MVC 模式的秘密不在于编写代码，而在于维护代码，并允许人们修改代码而无需更改太多其他内容。此外，请记住，不同的开发人员有不同的优势和劣势，因此围绕 MVC 进行团队构建更容易。想象一个视图团队负责创建出色的视图，一个模型团队非常了解数据，以及一个控制器团队负责了解应用程序流程的全局情况，处理请求，与模型协作，并为该客户端选择最合适的下一个视图。
例如：一个简单的中央数据库可以使用仅“模型”来组织，例如一个简单的数组。但是，稍后，使用链表可能更适用。所有数组访问都需要重新制作为相应的链表形式（例如，您将更改 myarray[5] 为 mylist.at(5)，或您使用的语言中的等效项）。
好吧，如果我们遵循 MVC 模式，中央数据库将使用某种函数进行访问，例如 myarray.at(5)。如果我们将模型从数组更改为链表，我们所要做的就是用模型更改视图，整个程序就改变了。保持界面相同，但更改其底层机制。这将允许我们比以前更自由、更快地进行优化。
模型-视图-控制器模式的优势之一显然是，在实现不同视图时能够重用应用程序的逻辑（在模型中实现）。一个很好的例子是在 Web 开发中，一个常见的任务是在现有软件中实现外部 API。如果 MVC 模式已遵循干净的模式，则这只需要修改控制器，控制器能够根据用户代理请求的内容类型呈现不同类型的视图。