weak reference

• 弱引用； 弱参考

weak reference的用法和样例：

例句

1. Create a short weak reference for the object.
   一般只需要短弱引用。
2. Synchronization blocks hold weak references to managed objects and must be scanned by the garbage collector.
   同步块保留对托管对象的弱引用并且必须由垃圾回收器扫描。