This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
Jar stands for "Java Archive" and it is really just a zipped file containing classes. You can execute a jar file from the command prompt if you supply a manifest file to tell the system which class has the main method in it that you want to start with. Here is a tutorial.
"JavaRanch, where the deer and the Certified play" - David O'Meara