If you want to create Java Program in Ubuntu, the first thing is to configuring JDK. And that what this page will tell you.

• JDK preparing

Above all, prepare a tar.gz JDK package. If you don't want to download it from the official website, a mirror website is a good choice: http://repo.huaweicloud.com/java/jdk.
You can use wget or VMware shared folders or even a U-disk to put it into your Ubuntu disk.

Ubuntu:~$ ls /home/user/temp
jdk-8u212-linux-x64.tar.gz

And here I prepared a jdk-8u212-linux-x64.tar.gz in /home/user/temp.

• Archive unpacking

Use the command:

Ubuntu:~$ tar -zxf /home/user/temp/jdk-8u212-linux-x64.tar.gz -C unpackpath

The parameter unpackpath after -C is to indicate the path of your unpacked files or folders.

• Environment variables configuration

Use the command:

Ubuntu:~$ sudo vim /etc/profile

open the file and add the following content to it:

JAVA_HOME=unpackpath/jdk1.8.0_212
CLASSPATH=$JAVA_HOME/lib/
PATH=$PATH:$JAVA_HOME/bin

and then use the command:

Ubuntu:~$ sudo source /etc/profile

to validate the modification.

• Configuration confirming

Use the command:

Ubuntu:~$ java -version

to confirm the jdk and java version, if you configured it successfully, the interface will be shown as:

java version "1.8.0_212"
Java(TM) SE Runtime Environment (Build 1.8.0_212-b10)
Java HotSpot(TM) 64Bit Server VM (build 25.212-b10, mixed mode)