黑马程序员-多线程-11天-3

/*
单例设计模式。

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

//懒汉式

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!");
}
}