Question about package dependencies, package versions and distro releases

[Severin Schoepke]

Hi list,

I have a question about the whole packaging system and I'd like to ask 
it with an example:

I have to do some Java coding for university and Java 6 which is 
(partially) open source has just been released. So I wanted to try it. 
At the moment I'm using Edgy and java-6-sun is not available for it, but 
it is packaged for Feisty already. I'm not so comfortable with 
installing software that is not packaged for Ubuntu, so I didn't want to 
install the JDK6 manually... So I did the following (I'm rather new to 
Linux and APT, so I have no idea if the following is a bad idea): I 
edited the sources.list the following way: I copied the line

deb http://ch.archive.ubuntu.com/ubuntu/ edgy main restricted universe 
multiverse

and changed it to

deb http://ch.archive.ubuntu.com/ubuntu/ feisty multiverse

This should give me access to the Feisty multiverse repository. After 
that I ran apt-get update and apt-get install sun-java6-jdk. Java 6 
installed flawlessly. After that, I removed the new line from 
sources.list and ran update-alternatives --config java. Now I have a 
working version of Java 6 that I could remove through Synaptic/apt-get 
if I want to...

Now to my questions:
- Is this 'bad' (using packages from another distro)?
- Packages don't seem to include information to which distro (e.g. Edgy 
or Feisty) they belong, or do they?
- Do packages depend 'just' on other packages or do they depend on a 
special version of other packages?
- Was I lucky that the above worked or should installing packages from 
other distro releases always work?
- Regarding the update from Edgy to Feisty: what is the difference 
between using apt-get dist-upgrade  and changing  all occurences of 
'edgy' to 'feisty' in sources.list and apt-get update && apt-get upgrade?

I hope someone can explain this stuff to me... Thanks in advance!

cheers, Severin