How does java/javac installation work in ubuntu?

[kevincmaker]

Recently I installed jdk 1.7 in ubuntu. These are the steps that I used to install it.

1. Extracted the folder named 'jdk1.7.0' and copied it to '/usr/lib/jvm'.

2. Installed javac using the following command
sudo update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/jdk1.7.0/bin/javac 4

3. Installed java using the following command
sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/jdk1.7.0/bin/java 4

I use Ubuntu 12.10

But, I really don't understand why I did all these things and how they work but they did. Can anyone explain how they work in Ubuntu?

Thanks in advance!

Regards,
Kevin.

[Pjotr123]

This is a more detailed how-to for installing Java manually:
https://sites.google.com/site/easylinuxtipsproject/java

With explanations of each command. :)