Mariusz Kumorek thinks this is interesting: If the Date values are not modified after they are placed in the Map, then the synchronization in the synchronizedMap implementation is sufficient to publish the Date values safely, and no additional synchronization is needed when accessing them. From Chapter 3. Sharing Objects from Java Concurrency in Practice by Doug Lea, David Holmes, Joseph Bowbeer, Joshua Bloch, Tim Peierls, Brian Goetz Publisher: Addison-Wesley Professional Released: May 2006 Note why? Share this highlight http://www.safaribooksonline.com/a/java-concurrency-in/14435738/ Twitter Facebook Google Plus Email Get Instant Access Now Start a Free Trial Have an account? Sign in. Minimise Unlock the rest of Java Concurrency in Practice and 30,000 other books and videos By clicking this box, you confirm that you have read and agree to the terms and conditions of our Membership Agreement, and you understand that when your trial period ends, you will be required to provide billing information if you wish to continue using the service. Unlock the rest of this book Start a Free 10-Day Trial loading Learn about Safari for Business Have an account? Sign in.