This is confusing.

Synaptic (note spelling) is the package manager for Debian based systems. It
handles packages which are maintained in the repositories for the
distribution. It has a graphical interface but does the same work as typing
commands such as sudo apt-get install package-name from the terminal.

To confuse matters even more there is more than one package manager for
Ubuntu (Adept and Packagekit to name but two). They all work basically the
same way, though.

The easiest way to get Java to work is to install the restricted-extras for
your distro. Each desktop has its own, ubuntu-restricted-extras or
kubuntu-restricted-extras, etc. This gives you Java, flash, mp3, MS core
fonts, DVD playing capabilities etc. See:
https://help.ubuntu.com/community/RestrictedFormats

In Synaptic just Search (not quick search!) for restricted-extras. Right
click on the correct one and choose Mark for Installation and click Apply.
You should have Java and flash and most things working for the web and
multimedia. However, it may not work in all browsers, Chromium for example.