There are no structural differences between the files; they are all archived using zip-jar compression. However, they are intended for different purposes.

--Jar files (files with a .jar extension) are intended to hold generic libraries of Java classes, resources, auxiliary files, etc.

--War files (files with a .war extension) are intended to contain complete Web applications. In this context, a Web application is defined as a single group of files, classes, resources, .jar files that can be packaged and accessed as one servlet context.

--Ear files (files with a .ear extension) are intended to contain complete enterprise applications. In this context, an enterprise application is defined as a collection of .jar files, resources, classes, and multiple Web applications.

Each type of file (.jar, .war, .ear) is processed uniquely by application servers, servlet containers, EJB containers, etc.