can an update over write java in /usr

[Tapas Mishra]

I am running a site which hosts an LMS known as Sakai
today morning I noticed my website down.(This problem is different
from my other upgrade thread)

I am investigating this problem as what are the possible reasons

As per the doc of sakai
https://confluence.sakaiproject.org/display/DOC/Sakai+2.7 (binary
section on this link)
  it needs following version of Java

java version "1.6.0_20"
Java(TM) SE Runtime Environment (build 1.6.0_20-b02-279-10M3065)
Java HotSpot(TM) 64-Bit Server VM (build 16.3-b01-279, mixed mode)

I observed that
	One week before the
	JAVA_HOME was /usr/lib/jvm/java-6-sun-1.6.0.20

	While today in the process of debugging this problem I notice that
there is no such 	directory

	/usr/lib/jvm/java-6-sun-1.6.0.20
	where as this did existed before doing any apt-get update

	Seems any update of Ubuntu has over written this.(Not sure of this though)

So is it possible that if a new version of Java is available in some
update it over writes my installation.
If that being the case how can I go back to the previous version it
does not exist there any more.
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