仅当所有线程在访问该集合前都锁定该对象时，同步才有效。

Synchronization is effective only if all threads lock this object before accessing the collection.

youdao

仅当所有线程在访问该集合前都锁定该对象时，同步才有效。

Synchronization is effective only if all threads lock this object before accessing the collection.

youdao