单实例

class Singleton
{
        private static Singleton instance;//类Feild：instance   
        private Singleton()//构造器 
        {}
        public static Singleton getInstance()//特殊方法，可以访问构造器
        {
                if (instance == null)
                {
                        intance = new Singleton();
                }
                return instance;
        }
}
public class SingleTest
{
        public static void main(String[] args)
        {
                Singleton s1 = Singleton.getInstance();
                Singleton s2 = Singleton.getInstance();
                System.out.println(s1==s2);
        }
}