Memory consistency effects in ConcurrentMap

According to the ConcurrentMap Javadoc:

Memory consistency effects: As with other concurrent collections, actions in a thread prior to placing an object into a ConcurrentMap as a key or value happen-before actions subsequent to the access or removal of that object from the ConcurrentMap in another thread.

What is the meaning of above statement? And how does it work as the get() method in ConcurrentHashMap is not blocking (compared to BlockingQueue for example)?