Hello Jude,
Sorry for the late reply, I'm on vacation till June 2nd and checking emails just now. I am using Mac OS X 10.6.8 and there are no new updates available under the "Software updates" so the latest Java update by apple is already installed and I see that it is update 15. I believe the Java update 21 you are referring to might be for some other OS.
I checked once again now and confirmed that there are no new Java updates.
Thanks for your response.