Install JDK9 in Ubuntu

Installation and Configuration of JDK9 is step by step given below:

Install JDK9 in Ubuntu:

sudo add-apt-repository ppa:webupd8team/java
sudo apt-get update
sudo apt-get install oracle-java9-installer

Make it as default:

sudo apt-get install oracle-java9-set-default

Changed in .bashrc, /etc/environment and also set default using

3 sections to change java configuration.

.bashrc:

export JAVA_HOME=/usr/lib/jvm/java-9-oracle
export PATH=$JAVA_HOME/bin:$PATH

/ect/environment:

JAVA_HOME="/usr/lib/jvm/java-9-oracle"
PATH=$PATH:$JAVA_HOME/bin

Then run the following command and set

sudo update-alternatives --config java

sudo update-alternatives --config javac

Then run the command

source /etc/environment

Check in terminal:

java -version
echo $JAVA_HOME
which java
which javac

Issue#1:

Execute "source /etc/environment" in every shell where you want the variables to be updated:

$ source /etc/environment

Resource Link: https://stackoverflow.com/a/5994031

Issue#2:

Just write JAVA_HOME="/usr/lib/jvm/java-9-oracle" on your /etc/environment, without the "export"

/etc/environment is supposed to contain a set of environment variables given as key=value pairs. It is not a shell script, so you can't use shell commands such as export in it.

Resource Link:

How to properly set JAVA_HOME in /etc/environment

Issue#3:

To check if java is properly installed:

$ which java

$ which javac

You should get similar output:

/usr/bin/java

Resource Link: https://stackoverflow.com/a/23124805

Issue#4:

To remove Oracle JDK completely, run the commands below:

Completely remove criteria:

sudo apt-get remove oracle-java9-installer
sudo apt-get remove --auto-remove oracle-java9-installer
sudo apt-get purge oracle-java9-installer
sudo apt-get purge --auto-remove oracle-java9-installer

Resource Link:

https://www.howtoinstall.co/en/ubuntu/trusty/tomcat7?action=remove