JAR(Java Archieve) File : JAR is a group of .class files. I mean it contains a group of .class files.

WAR(Web Archieve) File : WAR file represents generally a web application. Suppose i want to build a web application, then i have to use web related technologies, such as servlet, jsps, html, css, etc...

Then the total web application when i will deliver to client, then we convert into a single zip file, which is called as WAR file. As a result transportation will be easy, project delivery will be easy and project deployment will also be easy. So in reality, web applications are maintained in the form of WAR file.

EAR(Enterprise Archieve) File : Similarly an EAR file represents an enterprise application. To develop an enterprise application, we use anything from J2EE, such as servlets, jsps, EJB,JMS components etc...so to convert an total enterprise application into a single zip file is called as EAR file. Basically enterprise application deliver to client in the form of EAR file due to easy transportation, easy project delivery and easy project deployment