參考資料 https://www.digitalocean.com/community/tutorials/how-to-install-java-with-apt-get-on-ubuntu-16-04

Oracle JDK 9

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

Managing Java

sudo update-alternatives --config java

Setting the JAVA_HOME Environment Variable

sudo nano /etc/environment

Edit /etc/environment

JAVA_HOME="/usr/lib/jvm/java-9-oracle"

Save and exit the file, and reload it.

source /etc/environment

echo $JAVA_HOME