easy using update alternatives

While it is still very annoying in Linux to switch between different environment like JDK6 and JDK7, even though this is much easier than in Windows.
Now update-alternatives gives us a solution.

switch between different environements

Any installed kit and environment by apt-get will automatically registered in update-alternatives, which is in the folder of /etc/alternatives, you could see it has so many symbolic links, different links point to that bin command in real.
The strategy above ensured the flexibility to switch between different software and environment, you just need to use

sudo update-alternatives --config <name>

or

sudo update-alternatives --set <name> <bin_path>

to specify and switch to a new environment.

Notice --config is an interactive command hence is very user friendly, whilst --set have no prompt as to make it feasible to write script.

install or append new command

sudo update-alternatives --install <link> <name> <path> <priority>

where link is the path where your $PATH will included in, like /usr/bin/java.

name is the name registered in alternatives, where it shown in /etc/alternatives/<name>, like java.

path is the real command path where you can use this path to execute target command, like /usr/lib/jvm/java-8.0.5-oracle-amd64/bin/javac

priority will affect default choice of this command, you could browse others by update-alternatives --config <name> to have a comparison. with higher value means higher priority.

example:

sudo update-alternatives --install /usr/bin/javac    java /usr/lib/jvm/java-8.0.5-oracle-amd64/jre/bin/java   1000