A lot (if not all) of the JDK 1.6 concurrent classes are already part of the backport release. I'm not sure what classes in other packages are around. http://dcl.mathcs.emory.edu/util/backport-util-concurrent/compatibility.php Adrian, I think configuring the retro behavior by transformation class names is the most flexible, though I wonder if source and destination Java version would be sufficient. Was there any intention on generalizing the retro compiler into something that could be used for other purposes? View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3985895#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...