设计模式04：单例模式

单例模式，比较简单。UML如下

饿汉式：

public class Single {    private static Single single=new Single();    private Single(){}    public static Single getInstance(){        return single;    }}

懒汉式：方法体上需要加synchronized关键字

public class Singleton {      private static Singleton instance;      private Singleton (){}      public static synchronized Singleton getInstance() {      if (instance == null) {          instance = new Singleton();      }      return instance;      }  }