A Java Archive, or JAR file, contains all of the various components that make up a self-contained, executable Java application, deployable Java applet or, most commonly, a Java library to which any ...
Up until Java 2, a real-world project had a lot of infrastructure to build: what with class loaders, security, distributed lookup and communications, etc. Between JavaTM 1.1 and Java 2 Sun fleshed-out ...