Synchronization is built around an internal entity known as the intrinsic lock or monitor lock. (The API specification often refers to this entity simply as a "monitor.")
调用等待后,当前线程就要释放所持有的对象的锁,并且被添加到与该对象相关联的线程等待集合(Wait Set)中.等待其他线程在执行时调用此对象的notify() or notifyAll() 去唤醒Wait Set 中的某一个或者全部线程去重新竞争此对象的锁以执行run()方法.任何一个Object对象都有一个与它关联的锁对象(Lock or Monitor Lock),和一个线程等待集合(Wait Set).
