If you want this environment variable available to all users and on system start then you can add the following to /etc/profile.d/java.sh (create it if necessary):
export JDK_HOME=/usr/lib/jvm/java-7-oracle
export JAVA_HOME=/usr/lib/jvm/java-7-oracle
Then in a terminal run:
sudo chmod +x /etc/profile.d/java.sh
source /etc/profile.d/java.sh
My second question is - should it point to java-6-sun or java-6-sun-1.6.0.24 ?
It should always point to java-7-oracle as that symlinks to the latest installed one (assuming you installed Java from the Ubuntu repositories and now from the download available at oracle.com).
java 6
export JAVA_HOME=/usr/lib/jvm/java-1.6.0-openjdk-amd64
or java 7
export JAVA_HOME=/usr/lib/jvm/java-1.7.0-openjdk-amd64
to set Oracle's Java SE Development Kit as the system default Java just download the latest Java SE Development Kit from here then create a directory somewhere you like in your file system for example /usr/java now extract the files you just downloaded in that directory:
$ sudo tar xvzf jdk-8u5-linux-i586.tar.gz -C /usr/java
now to set your JAVA_HOME environment variable:
$ JAVA_HOME=/usr/java/jdk1.8.0_05/
$ sudo update-alternatives --install /usr/bin/java java ${JAVA_HOME%*/}/bin/java 20000
$ sudo update-alternatives --install /usr/bin/javac javac ${JAVA_HOME%*/}/bin/javac 20000
make sure the Oracle's java is set as default java by:
$ update-alternatives --config java
you get something like this:
There are 2 choices for the alternative java (providing /usr/bin/java).
Selection Path Priority Status
------------------------------------------------------------
* 0 /opt/java/jdk1.8.0_05/bin/java 20000 auto mode
1 /opt/java/jdk1.8.0_05/bin/java 20000 manual mode
2 /usr/lib/jvm/java-6-openjdk-i386/jre/bin/java 1061 manual mode
Press enter to keep the current choice[*], or type selection number:
pay attention to the asterisk before the numbers on the left and if the correct one is not set choose the correct one by typing the number of it and pressing enter. now test your java:
$ java -version
if you get something like the following, you are good to go:
java version "1.8.0_05"
Java(TM) SE Runtime Environment (build 1.8.0_05-b13)
Java HotSpot(TM) Server VM (build 25.5-b02, mixed mode)
also note that you might need root permission or be in sudoers group to be able to do this. I've tested this solution on both ubuntu 12.04 and Debian wheezy and it works in both of them.
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.
If you want to use specific version of Java when multiple JDKs are installed, just setting JAVA_HOME may not work.
You need to use sudo update-alternatives --config java to set default Java.
Refer to https://askubuntu.com/questions/121654/how-to-set-default-java-version.
If you're doing any sort of development you need to point to the JDK (Java Development Kit). Otherwise, you can point to the JRE (Java Runtime Environment).
The JDK contains everything the JRE has and more. If you're just executing Java programs, you can point to either the JRE or the JDK.
You should set JAVA_HOME based on current Java you are using.
readlink will print value of a symbolic link for current Java and sed will adjust it to JRE directory:
export JAVA_HOME=$(readlink -f /usr/bin/java | sed "s:bin/java::")
If you want to set up JAVA_HOME to JDK you should go up one folder more:
export JAVA_HOME=$(readlink -f /usr/bin/java | sed "s:jre/bin/java::")
If you want to change it globally and at system level;
In
/etc/environment
add this line:
JAVA_HOME=/usr/lib/jvm/java-7-oracle
Source: Stackoverflow.com