Head First 设计模式 （五） 单件模式（Singleton pattern） C++实现

单件模式确保一个类只有一个实例，并提供一个全局访问点。

确定在性能和资源上的限制，然后小心地选择适当的方案来实现单件，以解决多线程的问题。

代码链接：点击打开链接

单件模式类图：

源代码：

#ifndef CHOCOLATEBOILER_H
#define CHOCOLATEBOILER_H

#include<iostream>

class ChocolateBoiler
{
    private:
        ChocolateBoiler()
        {
            empty = true;
            boiled = false;
        }
        ~ChocolateBoiler()
        {
            uniqueInstance = 0;
        }
        ChocolateBoiler( const ChocolateBoiler& );
        void operator=( const ChocolateBoiler& );
    public:
        static ChocolateBoiler * getInstance()
        {
            if(uniqueInstance==0)
            {
                std::cout << "Creating unique instance of Chocolate Boiler" << std::endl;
                uniqueInstance = new ChocolateBoiler();
            }
            std::cout << "Returning instance of Chocolate Boiler"<< std::endl;
            return uniqueInstance;
        }
        void fill()
        {
            if(isEmpty())
            {
                empty = false;
                boiled =false;
            }
        }

        void drain()
        {
            if(!isEmpty() && isBoiled())
            {
                empty = true;
            }
        }

        void boil()
        {
            if(!isEmpty() && !isBoiled())
            {
                boiled = true;
            }
        }
        bool isEmpty()
        {
            return empty;
        }

        bool isBoiled()
        {
            return boiled;
        }
    protected:
    private:
        bool empty;
        bool boiled;
        static ChocolateBoiler* uniqueInstance;
};

#endif // CHOCOLATEBOILER_H

测试代码：

#include "ChocolateBoiler.h"

ChocolateBoiler* ChocolateBoiler::uniqueInstance = 0;
int main()
{
    ChocolateBoiler* boiler = ChocolateBoiler::getInstance();
    boiler->fill();
    boiler->boil();
    boiler->drain();

    ChocolateBoiler *boiler2= ChocolateBoiler::getInstance();
    if(boiler == boiler2)
        std::cout<<"Got same boiler"<<std::endl;
    else
        std::cout<<"Got different boler"<<std::endl;

    return 0;
}

测试结果如下：

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