I wish to test the new features that will came with the next JDK like project coin, project lambda etc. but the last JDK 7 to download will not have any already implemented!
From which build can I test them?
I think it's incredible that, now in may 2010 at few months to the official final release (november 2010????) for we developers there is no possibility to test any of this features!!
Take a look at the CAP program. In addition to the early release builds available for download via the normal download channels, you can also access the weekly snapshot builds.
You'll need to sign an Non-Disclosure Agreement though ...
EDIT
From browsing some messages in the lambda-dev mailing list, I get the impression that the implementation of closures in Java 7 may be suffering from "resourcing issues", and the (now) Oracle technical folks are not allowed to talk about it. That may explain why closures support is not showing up in the builds yet. If you signed up for CAP, you might be able to find out more. (And before you ask, no I haven't signed up and I don't have any inside information.)
You can get OpenJDK 7 / JDK 7 binary snapshot releases from http://download.java.net/jdk7/binaries/.