Running a Java program
On Mac OS X
Created with Java Version 8 (Update 73)


Save the program - Hello.class

Open the terminal app in Applications/Utilities

Go to the folder where you saved it using the cd (Change Directory) command
e.g. "cd Downloads"
type "/usr/bin/java Hello"

In Windows 10 :

Save the program - Hello.class 
 In Edge, IE or Firefox click on it and select save or keep.
 In Chrome right click and select "Save link as"

Press the windows logo key +R to get the run or search box
 or select the "Ask me anything" box on the bottom left.
Type "cmd.exe" (or just "cmd").
Go to the command processor/terminal/prompt/shell window you just opened.
Go to the folder you specified for downloads (Downloads is the default).
e.g. "cd C:\Users\User_name\Downloads" (change directory [cd] to Downloads)
Type "java Hello"  (Do not type "Hello.class")

I had a lot of trouble compiling and running Java.
Some things I tried.  I don't know which were required.
Download the latest JDK. Java SE Development Kit 8 - Downloads
I put "JAVA_HOME=/Library/Java" in my .profile
I and a lot of other people got the following when running:
  "Error: Could not create the Java Virtual Machine.
   Error: A fatal exception has occurred. Program will exit"
See How to fix "Could not create the Java Virtual Machine" Errorkombitz | kombitz

My problem was I was typing "java Hello.class" instead of "java Hello"

Links:
Verify Java Version
Java Downloads for All Operating Systems | Java.com
Java SE - Downloads | Oracle Technology Network | Oracle.com