Watch Joshua Bloch's Interview (17 min).
Joshua Bloch implemented the Java Collections Framework and is the author of Effective Java and Java Puzzlers. He now works at Google where he is in charge of all their Java infrastructure.
On Closures, Joshua comments:
I think closures in java are a good thing. We've basically had them since 1.1 in the form of anonymous class instances and those are a bit clunky so I definitely see a place for improvement support for closures; on the other hand some of the proposals that I've seen floating around are overly complex...If we add more support for closures I think it has to be in the spirit of the current support, which means that closures should take the form of instances, of types that have a single abstract method, whether they are interface types such as Runnable , or class types such as TimerTask...