Java missing in Software Updater

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I have Java Standard Edition installed on my system, but it is not shown in the application list of Software Updater. Neither "Refresh" nor "Database reset" helps.
This situation happened long time (at least one year) and I thought that Avast simply neglected Java.
But now I installed Avast to another computer and Software Updater shows Java there.

The software installed on both computers:
Windows XP Pro 32 bit
Java Standard Edition 8 Update 31 (up to date now; anyway the problem occured with earlier versions too)
Avast Free Antivirus 2015.10.0.2208 (up to date now; anyway the problem occured with earlier versions too)

[Eddy]

http://www.java.com/en/download/help/sysreq.xml

According to the system requirements java 8 doesn't run on Windows XP

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1) Java 8 does run on Windows XP:

The software installed on both computers (incl. the one without problems):
...
Java Standard Edition 8 Update 31 (up to date now; anyway the problem occured with earlier versions too)

2) Oracle doesn't say that Java 8 doesn't run on Windows XP. It says it runs but it is not supported (there is a warning prior installation).

3) The problem appeared even with Java 7.