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copied!<blockquote> <p>In this scenario, are the members of the ArrayList as seen by Thread B guaranteed to be at least as up to date as they were when MyClass's constructor completed?</p> </blockquote> <p>Yes, they are.</p> <p>A thread is required to read memory when it encounters reference for the first time. Because hash map is constructed, all entries in it are brand new, then the references to objects are <code>up-to-date</code> to what they were when the constructor has finished.</p> <p>After that initial encounter, the usual visibility rules apply. So, when other thread changes non-final field in the final references, the other thread may not see that change, but it still will see the reference that came out of constructor.</p> <p>In reality, it means that if you do not modify final hash-map after the constructor, its contents are constants for all threads.</p> <p><strong>EDIT</strong></p> <p>I knew that I've seen this guarantee somewhere before.</p> <p>Here is a paragraph of interest from this <a href="http://www.ibm.com/developerworks/library/j-jtp03304/" rel="noreferrer">article</a> that describes JSR 133</p> <blockquote> <p><strong>Initialization safety</strong></p> <p>The new JMM also seeks to provide a new guarantee of initialization safety -- that as long as an object is properly constructed (meaning that a reference to the object is not published before the constructor has completed), then all threads will see the values for its final fields that were set in its constructor, regardless of whether or not synchronization is used to pass the reference from one thread to another. Further, any variables that can be reached through a final field of a properly constructed object, such as fields of an object referenced by a final field, are also guaranteed to be visible to other threads as well. This means that if a final field contains a reference to, say, a LinkedList, in addition to the correct value of the reference being visible to other threads, also the contents of that LinkedList at construction time would be visible to other threads without synchronization. The result is a significant strengthening of the meaning of final -- that final fields can be safely accessed without synchronization, and that compilers can assume that final fields will not change and can therefore optimize away multiple fetches.</p> </blockquote>

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