澄清Object类中的finalize（）方法(Clarification on finalize() method in Object class)

 如果有人能够在Object类的finalize（）方法的javadoc中正确地澄清2点，那将会很有帮助： 
 
1. It is guaranteed, however, that the thread that invokes finalize will not be holding any user-visible synchronization locks when finalize is invoked.
 
 “用户可见”同步的意义是什么？ 除了“用户可见”之外还有其他同步吗？ 
 
2. The finalize method is never invoked more than once by a Java virtual machine for any given object.
 
 在这种情况下，JVM必须保持所创建的每个对象的唯一标识与已调用其finalize方法的信息。 难道它最终会超越它存储的任何区域吗？ 

It'd be helpful if anyone could clarify properly on the 2 points from javadoc of finalize() method in Object class:
 
1. It is guaranteed, however, that the thread that invokes finalize will not be holding any user-visible synchronization locks when finalize is invoked.
 
What is the significance of 'user-visible' synchronization? Are there any other synchcronization apart from 'user-visible'?
 
2. The finalize method is never invoked more than once by a Java virtual machine for any given object.
 
In that case, JVM must maintain unique identity of each and every object ever created vs the information that its finalize method has been invoked. Wouldn't it ultimately grow beyond whatever region it is stored in ?

原文：https://stackoverflow.com/questions/23359753