设计模式读书笔记
策略模式
Strategy模式可以用来替换if else
class TaxStrategy{
public:
virtual double Calculate(const Context & context) = 0;
virtual ~TaxStrategy(){}
};
class SalesOrder{
private:
TaxStrategy* strategy;
public:
SalesOrder(StrategyFactory* strategyFactory){
this->strategy = strategyFactory->NewStrategy();
}//其实这个是工厂模式
~SalesOrder(){
delete this->strategy;
}
public double CalculateTax(){
Context context();
double val =
strategy->Calculate(context);
}
};
观察者模式
Observer/Event
通知依赖关系
所有的依赖对象都将得到通知ß
class MainForm: public Form, public IProgress{
TextBox * txtFilePath;
TextBox* txtFileNumber;
ProgressBar* progressBar;
public:
void Button1_Click(){
string filePath = txtFilePath->getText();
int number = atoi(txtFileNumber->getText().c_str());
FileSplitter splitter(filePath, number);
splitter.split();
}
virtual void DoProgress(float value){
progressBar->setValue(value);
};
};
class IProgress{
public:
virtual void DoProgress(float value) = 0;
virtua ~IProgress(){};
};//实现一个抽象的通知机制
class FileSplitter{
string m_filePath;
int m_fileNumber;
/*
假设要加入一个通知，通知进度如何
加入一个抽象通知机制
*/
IProgress * m_iprogress;
public:
FileSplitter(const string & filePath, int fileNumber):m_filePath(filePath),m_fileNumber(fileNumber),m_iprogress(iprogress){}
void split(){
for(int i = 0 i < m_fileNumber; i ++){
.....
if(m_iprogress != nullptr){
float progressValue = m_fileNumber;
progressValue = (i + 1) / progressValue;
m_iprogress->DoProgress(progressValue);
}
}
}
};
工厂模式
Factory Method
对象创建模式
绕开new，来避免对象创建过程中的紧耦合
面向接口的编程
new带来了细节依赖
class MainForm:public Form{
private:
TextBox * txtFilePath;
TextBox* txtFileNumber;
ProgressBar* progressBar;
splitterFactory * factory;
public:
MainForm(splitterFactory * factory){
this->factory = factory;
}
void Button1_Click(){
ISplitter * splitter =
factory->CreateSplitter();
splitter->split();
}
};
class ISplitter{
public:
virtual void split() = 0;
~ISplitter(){};
};
//具体类
class FileSplitter : public ISplitter{
public:
void split(){
}
};
class BinarySplitter: public ISplitter{
};
class TxtSplitter : public ISplitter{
};
class videoSplitter: public ISplitter{
};
class SplitterFactory{
public:
virtual ISplitter * CreateSplitter() = 0;
virtual ~SplitterFactory(){};
};
//具体工厂
class BinarySplitterFactory: public SplitterFactory{
public:
virtual ISplitter * CreateSplitter(){
return new BinarySplitter();
}
}
抽象工厂
Abstract Factory
经常面对一些相互依赖的对象的创建工作
提供一个接口，让该接口负责创建一系列“相关或者相互依赖的对象”
无需指定它们具体的类
class IDBConnection{
};
class IDBCommand{
};
class IDataReader{
};
class IDBConnectionFactory{//工厂类
public:
virtual IDBConnection * CreateDBConnection() = 0;
};
class sqlConnectionFacory : public IDBConnectionFactory{//具体的工厂实现
public:
virtual IDBConnection * CreateDBConnection(){
return new SqlConnection();
}
};
class SqlConnection : public IDBConnection{
};
class sqlCommand: public IDBCommand{
};
class IDBCommandFactory{
public:
virtual IDBCommand * CreateDBCommand() = 0;
};
class sqlCommandFactory : public IDBCommandFactory{
public:
virtual IDBCommand * CreateDBCommand(){
return new sqlCommand();
}
};
class sqlReader : public IDataReader{
};
class IDBDataReaderFactory{
public:
virtual IDataReader * CreateDBReader()=0;
};
class sqlDataReaderFactory: public IDBDataReaderFactory{
public:
virtual IDataReader * CreateDBReader(){
return new sqlReader();
}
};
/*
省去了对应的mysql，oracle
*/
class EmployeeDAO{
IDBConnectionFactory * dbConnectionFactory;
IDBCommandFactory * dbCommandFactory;
IDBDataReaderFactory * dbReaderFactory;
//这几个对应的参数应该是同一类
public:
vector<EmployeeDO> GetEmployees(){
IDBCConnection * connection =
dbConnectionFactory->CreateDBConnection();
connection->ConnectionString = "...";
IDBCommand * command =
dbCommandFactory->CreateCreateCommand();
/*
其他的也一样是对应的实现
*/
}
};
//**********************************分割
/*
将三个合在一起
IDBConnectionFactory * dbConnectionFactory;
IDBCommandFactory * dbCommandFactory;
IDBDataReaderFactory * dbReaderFactory;
合成一个工厂
IDBFactory
*/
Singleton 单例模式
“对象性能”模式
面向对象很好的解决了“抽象”的问题，但是必不可免地要付出一定的代价。
在软件系统中，经常有这样一些特殊的类，必须保证它们在系统中只存在一个实例
才能确保它们的逻辑正确性，以及良好的效率
class Singleton{
private:
Singleton();
Singleton(const Singleton & other);
public:
static Singleton * getInstance();
static Singleton * m_instance;
};
Singleton * Singleton::m_instance=nullptr;
//线程非安全版本 单线程可行
Singleton * Singleton::getInstance(){
/*
假设存在两个线程 prthead_A, prthead_B
A走到new这一步 ， 时间片轮转到B这一步
然后就并发了
*/
if(m_instance == nullptr){
m_instance = new Singleton();
}
return m_instance;
}
//同步的懒汉模式 线程安全版本 互斥锁
Singleton * Singletion::getInstance(){
Lock lock;
if(m_instance == nullptr){
m_instance = new Singleton();
}
return m_instance;
}
//线程安全版本,但由于内存读写reorder不安全
/*
在cpu指令层次 new三次会被reorder
乱序处理
就是不按照 我们想象的三步来处理
双重检查懒汉模式
*/
Singleton * Singletion::getInstance(){
if(m_instance == nullptr){
Lock lock;
if(m_instance == nullptr)
m_instance = new Singleton();
}
return m_instance;
}
//C++ 11版本之后的跨平台实现(bolatile)
std::atomic<Singleton*> Singleton::m_instance;
std::mutex Singleton::m_mutex;
Singleton * Singleton::getInstance(){
Singleton * tmp = m_instance.load(std::memory_order_relaxed);
std::atomic_thread_fence(std::memory_order_acquire);
if(tmp == nullptr){
st::lock_guard<std::mutex> lock(m_mutex);
tmp = m_instance.load(std::memory_order_relaxed);
if(tmp == nullptr){
tmp = new Singletion;
std::atomic_thread_fence(std::memory_order_release);
m_instance.store(tmp, std::memory_order_relaxed);
}
}
return tmp;ge
}
class Singleton1{//饿汉模式
private:
Singleton1();
Singleton1(const Singleton & other);
static Singleton1 * m_instance = new Singleton1();
public:
static Singleton1 * getInstance();
};
static Sigleton1 Sigleton1::getInstance(){
return m_instance;
}
