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.
People often say "blah blah is a service written in java". Blah blah can be started and stoped by usually executing scripts. What does a service exactly mean ? why not just pack this service into a jar file so that everybody can use ? what's the difference between a service and a packed .jar including all service's code ?
Service is a very broad term that can mean all kinds of things; it sounds as if you're talking about a simple server. That would probably come in a jar file as well, so I'm not sure where you see the difference between the two.