黑馬程式員-多線程-11天-3

/*
單例設計模式。


*/
//餓漢式。
/*
class Single
{
    private static final Single s = new Single();
    private Single(){}
    public static Single getInstance()
    {
        return s;
    }
}
*/


//懶漢式

class Single
{
    private static Single s = null;
    private Single(){}


    public static  Single getInstance()
    {
        if(s==null)
        {
            synchronized(Single.class)
            {
                if(s==null)
                    //--->A;
                    s = new Single();
            }
        }
        return s;
    }
}

class SingleDemo 
{
    public static void main(String[] args) 
    {
        System.out.println("Hello World!");
    }
}      

轉載于:https://www.cnblogs.com/guwenren/archive/2013/04/07/3006389.html