/*

两种单例模式的演示

*/

//饿汉式

class  Signal

{

	private Signal(){}

	private Signal s = new Signal();

	public static Signal getInstance()

	{

		return s;

	}

}

//懒汉式

class Signal

{

	private Signal(){}

	private Signal s = null;

	public static Signal getInstance()

	{

		if(s == null)

		{

			synchronized(Signal.clss)

			{

				if(s == null)

					s = new Signal();

			}

		}

		return s;

	}

}

//记录原则：定义单例，建议使用饿汉式。