Find out whether you are running a 32 bit or a 64 bit OS:
uname -m
x86_64: 64 bit kernel
i686: 32 bit kernel
Go to the Oracle Java SE website and decide which version you want to install:
JDK: Java Development Kit. Includes a complete JRE plus tools for developing, debugging, and monitoring Java applications.
Server JRE: Java Runtime Environment. For deploying Java applications on servers. Includes tools for JVM monitoring and tools commonly required for server applications.
Accept the license and copy the download link into your clipboard. Remember to choose the right tar.gz (64 or 32 bits). Use wget to download the archive into your server:
wget --header "Cookie: oraclelicense=accept-securebackup-cookie" http://download.oracle.com/otn-pub/java/jdk/8u5-b13/jdk-8u5-linux-x64.tar.gz
Oracle does not allow downloads without accepting their license, therefore we needed to modify the header of our request. Alternatively, you can just download the compressed file using your browser and manually upload it using a SFTP/FTP client.
Always get the latest version from Oracle`s website and modify the commands from this tutorial accordingly to your downloaded file.
Installing Oracle JDK
The /opt directory is reserved for all the software and add-on packages that are not part of the default installation. Create a directory for your JDK installation:
sudo mkdir /opt/jdk
and extract java into the (/opt/jdk) directory:
sudo tar -zxf jdk-8u5-linux-x64.tar.gz -C /opt/jdk
Verify that the file has been extracted into the /opt/jdk directory.
ls /opt/jdk
Setting Oracle JDK as the default JVM
In our case, the java executable is located under /opt/jdk/jdk1.8.0_05/bin/java . To set it as the default JVM in your machine run:
update-alternatives --install /usr/bin/java java /opt/jdk/jdk1.8.0_05/bin/java 100
and
update-alternatives --install /usr/bin/javac javac /opt/jdk/jdk1.8.0_05/bin/javac 100
Verify your installation
Verify that java has been successfully configured by running:
update-alternatives --display java
and
update-alternatives --display javac
The output should look like this:
java - auto mode
link currently points to /opt/jdk/jdk1.8.0_05/bin/java
/opt/jdk/jdk1.8.0_05/bin/java - priority 100
Current 'best' version is '/opt/jdk/jdk1.8.0_05/bin/java'.
javac - auto mode
link currently points to /opt/jdk/jdk1.8.0_05/bin/javac
/opt/jdk/jdk1.8.0_05/bin/javac - priority 100
Current 'best' version is '/opt/jdk/jdk1.8.0_05/bin/javac'.
Another easy way to check your installation is:
java -version
The output should look like this:
java version "1.8.0_05" Java(TM) SE Runtime Environment (build 1.8.0_05-b13) Java HotSpot(TM) 64-Bit Server VM (build 25.5-b02, mixed mode
(Optional) Updating Java
To update Java, simply download an updated version from Oracle`s website and extract it under the /opt/jdk directory, then set it up as the default JVM with a higher priority number (in this case 110):
update-alternatives --install /usr/bin/java java /opt/jdk/jdk.new.version/bin/java 110
update-alternatives --install /usr/bin/javac javac /opt/jdk/jdk.new.version/bin/javac 110
You can keep the old version or delete it:
update-alternatives --remove java /opt/jdk/jdk.old.version/bin/java
update-alternatives --remove javac /opt/jdk/jdk.old.version/bin/javac
rm -rf /opt/jdk/jdk.old.version
Grabbed From : Ask Ubuntu