检索被引用对象的风格(WeakReference)

Ref: http://blog.youkuaiyun.com/zhangzhaokun/article/details/5083415

BAD！

obj = wr.get();

if (obj == null)

{

  wr= new WeakReference(recreateIt());  //1

  obj= wr.get();                        //2

}

//code that works with obj

行1之后，行2之前，有可能运行垃圾回收。若在行1之后执行了垃圾回收，通过recreateIt()创建的对象被回收，则行2中获得的对象将为null。

GOOD！

obj = wr.get();

if (obj == null)

{

  obj= recreateIt();                    //1

  wr= new WeakReference(obj);           //2

}

//code that works with obj