To install Java JDK 8 

1. Add A Third Party PPA to Ubuntu

ubuntu@skubuntu:/Store/Software/Linux$  sudo add-apt-repository ppa:webupd8team/java

[sudo] password for ubuntu:

Press Enter 

Output:

 Oracle Java (JDK) Installer (automatically downloads and installs Oracle JDK8). There are no actual Java files in this PPA.

- http://www.webupd8.org/2012/09/install-oracle-java-8-in-ubuntu-via-ppa.html
- Oracle Java 8: http://www.webupd8.org/2014/03/how-to-install-oracle-java-8-in-debian.html
 More info: https://launchpad.net/~webupd8team/+archive/ubuntu/java
Press [ENTER] to continue or Ctrl-c to cancel adding it.
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Reading package lists... Done
ubuntu@skubuntu:/Store/Software/Linux$

ubuntu@skubuntu:/Store/Software/Linux$ sudo apt update
Press Enter
Left Arrow Key then Press Enter #####Important########
To set Oracle JDK8 as default, install the "oracle-java8-set-default" package.
E.g.: sudo apt install oracle-java8-set-default
On Ubuntu systems, oracle-java8-set-default is most probably installed
automatically with this package.
###################### /usr/bin/java

java version "1.8.0_191"
Java(TM) SE Runtime Environment (build 1.8.0_191-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.191-b12, mixed mode)

x

x

Important -> Why Oracle Java 7 And 6 Installers No Longer Work: http://www.webupd8.org/2017/06/why-oracle-java-7-and-6-installers-no.html

Update: Oracle Java 9 has reached end of life: http://www.oracle.com/technetwork/java/javase/downloads/jdk9-downloads-3848520.html

The PPA supports Ubuntu 18.10, 18.04, 16.04, 14.04 and 12.04.

More info (and Ubuntu installation instructions):

Debian installation instructions:

For Oracle Java 11, see a different PPA -> https://www.linuxuprising.com/2018/10/how-to-install-oracle-java-11-in-ubuntu.html

Get:1 http://ppa.launchpad.net/webupd8team/java/ubuntu bionic InRelease [15.4 kB]

2. Update and install Oracle Java 8 on Your machine

ubuntu@skubuntu:/Store/Software/Linux$ sudo apt install oracle-java8-installer

ubuntu@skubuntu:/Store/Software/Linux$ which java

ubuntu@skubuntu:/Store/Software/Linux$ java -version

ubuntu@skubuntu:/Store/Software/Linux$