See this; run

sudo  update-java-alternatives --list

to list off all the Java installations on a machine by name and directory, and then run

sudo  update-java-alternatives --set [JDK/JRE name e.g. java-8-oracle]

to choose which JRE/JDK to use.

If you want to use different JDKs/JREs for each Java task, you can run update-alternatives to configure one java executable at a time; you can run

sudo  update-alternatives --config java[Tab]

to see the Java commands that can be configured (java, javac, javah, javaws, etc). And then

sudo  update-alternatives --config [javac|java|javadoc|etc.]

will associate that Java task/command to a particular JDK/JRE.

You may also need to set JAVA_HOME for some applications: from this answer you can use

export JAVA_HOME=$(readlink -f /usr/bin/java | sed "s:bin/java::")

for JREs, or

export JAVA_HOME=$(readlink -f /usr/bin/java | sed "s:jre/bin/java::")

for JDKs.

I think you should take a look at the update-java-alternatives command from the java-common package and the *.jinfo files used by it. With that you should be able to switch completely between java installations (regardless of JDK, JRE, ...).

On ubuntu/linux you can switch java version using

update-alternatives --config java

But before, you need install the version.

You can use this script (./install-java.sh) to install multiple JVMs

#!/bin/sh
(
lookforJdks=$PWD
echo "Directory: $lookforJdks"
jdks=`test -e ./javac || find $lookforJdks -type d -iname '*jdk1.*' 2> /dev/null`
#set -e
echo 'which jdk do you want to choose? looking for jdks. This might take a while'
echo "$jdks" | awk '{printf("%5d : %s\n", NR,$0)}'
read choose
test -e ./javac || cd `echo "$jdks" | tr '\n' ',' | cut -d',' -f $choose`/bin
for e in appletviewer extcheck idlj jar jarsigner java javac javadoc javah javap jconsole \
 jdb jhat jinfo jmap jps jrunscript jsadebugd jstack jstat jstatd native2ascii rmic \
 schemagen serialver wsgen wsimport xjc jvisualvm jmc; do sudo update-alternatives \
 --install /usr/bin/$e $e $(readlink -f ./$e) 100; done
)

echo "RUN update-alternatives --config java"

Put this script in folder where has unpacked the JVM(s), and run:

/opt/install-java.sh

Next use:

update-alternatives --config java

If you are going to manualy set alternatives for javac javaws javadoc or any other java related commands, you might want to make them slaves of the java altenative.

sudo update-alternatives --install "/usr/bin/java" "java" "/opt/jdk1.8.0_74/bin/java" 0 --slave "/usr/bin/javadoc" "javadoc" "/opt/jdk1.8.0_74/bin/javadoc"


update-alternatives: updating alternative /opt/jdk1.8.0_74/bin/java because link group java has changed slave links


:/opt/jdk1.8.0_74$ sudo update-alternatives --display java

java - auto mode link best version is /opt/jdk1.8.0_74/bin/java link currently points to /opt/jdk1.8.0_74/bin/java link java is /usr/bin/java slave javadoc is /usr/bin/javadoc /opt/jdk1.8.0_74/bin/java - priority 0 slave javadoc: /opt/jdk1.8.0_74/bin/javadoc

Change /opt/jdk1.8.0_74/ with the dir where your jdk is installed.

Open /etc/environment in any your text editor and add the following line:

JAVA_HOME="usr/lib/jvm/open-jdk 

- Java path could be diffrent.
Use source to load the variables, by running this command:

source /etc/environment

Then check the variable, by running this command:

echo $JAVA_HOME

With this path set, run this command:

sudo  update-java-alternatives --list

Choose your default Java Version.