Java Installation

There are several implementation of Java, one currently controlled by Oracle and it can be downloaded from but as far as I know there are various problematic licensing restrictions. A better choice is to download the Open JDK.
On MS Windows install it by unipping the .zip file and then configuring the PATH to include the bin/ directory.
Before we even write a line of code we would like to make sure that both the java compiler and the java runtime is accessible for us. So we open a command line window or a Power Shell window and we type in javac --version and java --version respectively.

On MS Windows

> javac --version
javac 14.0.2

> java --version
openjdk 14.0.2 2020-07-14
OpenJDK Runtime Environment (build 14.0.2+12-46)
OpenJDK 64-Bit Server VM (build 14.0.2+12-46, mixed mode, sharing)

On Ubuntu Linux:

$ javac -version
javac 1.8.0_252

$ java -version
openjdk version "1.8.0_252"
OpenJDK Runtime Environment (build 1.8.0_252-8u252-b09-1ubuntu1-b09)
OpenJDK 64-Bit Server VM (build 25.252-b09, mixed mode)