常用的两种单例模式

//懒汉式单例类.在第一次调用的时候实例化自己   public class Singleton {      private Singleton() {}      private static Singleton single=null;      //静态工厂方法       public static Singleton getInstance() {           if (single == null) {                 single = new Singleton();           }            return single;      }  }  //饿汉式单例类.在类初始化时，已经自行实例化   public class Singleton1 {      private Singleton1() {}      private static final Singleton1 single = new Singleton1();      //静态工厂方法       public static Singleton1 getInstance() {          return single;      }  }