Windows Command Prompt

Command Prompt result after "Java -version"

JRE (Java Runtime Environment) Installation Guide for Windows Operating System

As I mentioned in Windows System Requirements for Shaz Invice Software and Shaz Cash Receipt, you need to have JRE in your computer to be able to run a Java Application such as Shaz Invoice Software. I give a link above for JRE 1.6 that you can install it for Windows Operating System up to Windows 7 from my website, it will setup the Classpath by itself in Windows XP (it might does the setup by itself for all Windows operating system up to and including Windows XP), but you need to setup the Classpath manually for Windows 7 if you use this version. For Windows 8 and 10 please visit Oracle Website to find what version of JRE is compatible with your system and download it and install it. You might start from this link in oracle
The installation program with .exe extension is easier to install because the installer install the program without much interaction by the user. However to run a Java application, JRE must be seen globally in any directory in your System, as you see in image above which is a windows command prompt screenshot. (You can access command prompt screen from windows Accessories menu) Another words when you type "java -version" in any directory on windows command prompt screen you have to have a line similar to “Java(TM) SE Runtime Environment (build 1.6.0_26-b03)”, obviously in regards to your version of JRE.
If you do not have some lines as above or you get a message that Java or JRE does not exist, this means you need to setup your windows Classpath to point to your JRE folder. The best way is to search Internet with a search term such as "JRE Classpath setup for Windows 7" to find a guide for your system. You may visit this link
for Windows 10, however it gives installation guide for Java and JRE, but to run a a Java Application you only need JRE in your system. Next two links are for Windows 7 environment variables setup.
and last one for Windows 8
Also you must restart your Computer after changes done to system Classpath to invoke changes.