I normally set paths in
~/.bashrc
However for Java, I followed instructions at https://askubuntu.com/questions/55848/how-do-i-install-oracle-java-jdk-7
and it was sufficient for me.
you can also define multiple java_home's and have only one of them active (rest commented).
suppose in your bashrc file, you have
export JAVA_HOME=......jdk1.7
#export JAVA_HOME=......jdk1.8
notice 1.8 is commented. Once you do
source ~/.bashrc
jdk1.7 will be in path.
you can switch them fairly easily this way. There are other more permanent solutions too. The link I posted has that info.