Installing Oracle JAVA JDK
Run below command to one by one to install JAVA JDK.
#apt-get install python-software-properties
#add-apt-repository ppa:webupd8team/java
#apt-get update
To Install JDK6 Run below Command
#apt-get install oracle-java6-installer
To Install JDK7 Run below Command
#apt-get install oracle-java7-installer
To Install JDK8 Run below Command
#apt-get install oracle-java8-installer
Installation of JAVA JDK is Over !!!
Managing Java
When there are multiple Java installations on your ubuntu, the Java version to use as default can be chosen. To do this, execute the following command:
#update-alternatives --config java
It will usually return something like this if you have 2 installations (if you have more, it will of course return more):
There are 2 choices for the alternative java (providing /usr/bin/java).
Selection Path Priority Status
------------------------------------------------------------
* 0 /usr/lib/jvm/java-7-oracle/jre/bin/java 1062 auto mode
1 /usr/lib/jvm/java-6-oracle/jre/bin/java 1061 manual mode
Press enter to keep the current choice[*], or type selection number:
You can now choose the number to use as default. This can also be done for the Java compiler (javac):
#update-alternatives --config javac
It is the same selection screen as the previous command and should be used in the same way. This command can be executed for all other commands which have different installations. In Java, this includes but is not limited to: keytool, javadoc and jarsigner.
Setting the "JAVA_HOME" environment variable
To set the JAVA_HOME environment variable, which is needed for some programs, first find out the path of your Java installation:
#update-alternatives --config java
It returns something like:
There are 2 choices for the alternative java (providing /usr/bin/java).
Selection Path Priority Status
------------------------------------------------------------
* 0 /usr/lib/jvm/java-7-oracle/jre/bin/java 1062 auto mode
1 /usr/lib/jvm/java-6-oracle/jre/bin/java 1061 manual mode
Press enter to keep the current choice[*], or type selection number:
The path of the installation is for each:
/usr/lib/jvm/java-7-oracle
/usr/lib/jvm/java-6-oracle
Copy the path from your preferred installation and then edit the file /etc/environment:
#nano /etc/environment
In this file, add the following line (replacing YOUR_PATH by the just copied path):
JAVA_HOME=/usr/lib/jvm/java-7-oracle
That should be enough to set the environment variable. Now reload this file:
#source /etc/environment
Test it by executing:
#echo $JAVA_HOME
