Problem 1: Java version 7 is not available from Ubuntu repositories for your Ubuntu version (prior to 11.10 Oneiric). You don’t see it neither via
"Ubuntu Software Center"nor via
"Synaptic Package Manager".
What to do: Download JDK 7 binaries from the official Java site.
Problem 2: You are Debian/Ubuntu user and don’t see applicable
What to do: Again, download JDK 7 binaries from the official Java site, install and configure it manually.
Step by step instructions to install and manual configure JDK 7 on the Ubuntu 10.04 LTS (the Lucid Lynx) desktop follow: