单例模式在Java语言中，有两种构建方式

• 懒汉方式。指全局的单例实例在第一次被使用时构建。
• 饿汉方式。指全局的单例实例在类装载时构建。

在Java编程语言中，单例模式(饿汉模式)应用的例子如下述代码所示：

  public class Singleton {
    private final static Singleton INSTANCE = new Singleton();
 
    // Private constructor suppresses   
    private Singleton() {}
 
    // default public constructor
    public static Singleton getInstance() {
        return INSTANCE;
    }
  }

在Java编程语言中，单例模式(懒汉模式)应用的例子如下述代码所示 (此种方法只能用在JDK5及以后版本(注意 INSTANCE 被声明为 volatie)，之前的版本使用“双重检查锁”会发生非预期行为^[1])：

  public class Singleton {
    private static volatile Singleton INSTANCE = null;
 
    // Private constructor suppresses 
    // default public constructor
    private Singleton() {}
 
    //thread safe and performance  promote 
    public static  Singleton getInstance() {
        if(INSTANCE == null){
             synchronized(Singleton.class){
                 //when more than two threads run into the first null check same time, to avoid instanced more than one time, it needs to be checked again.
                 if(INSTANCE == null){ 
                     INSTANCE = new Singleton();
                  }
              } 
        }
        return INSTANCE;
    }
  }

在C++编程语言中，单例模式应用的例子如下述代码所示（这里仅仅提供一个示例，这个例子对多线程的情况并不是安全的）：

// ...
 
class lock
{
    public:
        lock();
        lock(lock const & l);
        ~lock();
        lock & operator =(lock const & l);
        void request();
        void release();
    // ...
};
 
lock::lock()
{
    // ...
}
 
// ...
 
lock::~lock()
{
    // ...
}
 
// ...
 
void lock::request()
{
    // ...
}
 
void lock::release()
{
    // ...
}
 
// ...
 
// assumes _DATA_TYPE_ has a default constructor
template<typename _DATA_TYPE_>
class singleton
{
    public:
        static _DATA_TYPE_ * request();
        static void release();
 
    private:
        singleton();
        singleton(singleton<_DATA_TYPE_> const & s);
        ~singleton();
        singleton<_DATA_TYPE_> & operator =(singleton<_DATA_TYPE_> const & s);
        static _DATA_TYPE_ * pointer;
        static lock mutex;
    // ...
};
 
template<typename _DATA_TYPE_>
_DATA_TYPE_ * singleton<_DATA_TYPE_>::pointer = 0;
 
template<typename _DATA_TYPE_>
lock singleton<_DATA_TYPE_>::mutex;
 
template<typename _DATA_TYPE_>
_DATA_TYPE_ * singleton<_DATA_TYPE_>::request()
{
    if(singleton<_DATA_TYPE_>::pointer == 0)
    {
        singleton<_DATA_TYPE_>::mutex.request();
 
        if(singleton<_DATA_TYPE_>::pointer == 0)
        {
            singleton<_DATA_TYPE_>::pointer = new _DATA_TYPE_;
        }
 
        singleton<_DATA_TYPE_>::mutex.release();
    }
 
    return singleton<_DATA_TYPE_>::pointer;
}
 
template<typename _DATA_TYPE_>
void singleton<_DATA_TYPE_>::release()
{
    if(singleton<_DATA_TYPE_>::pointer != 0)
    {
        singleton<_DATA_TYPE_>::mutex.request();
 
        if(singleton<_DATA_TYPE_>::pointer != 0)
        {
            delete singleton<_DATA_TYPE_>::pointer;
 
            singleton<_DATA_TYPE_>::pointer = 0;
        }
 
        singleton<_DATA_TYPE_>::mutex.release();
    }
}
 
template<typename _DATA_TYPE_>
singleton<_DATA_TYPE_>::singleton()
{
    // ...
}
 
// ...
 
int main()
{
    int * s;
 
    s = singleton<int>::request();
 
    // ...
 
    singleton<int>::release();
 
    return 0;
}