can someone explain why .jar files's base name archive

Question

.jar files

Answer 1

Usually applications deals with many number of Java class files. Then it will become very difficult in maintaining the files if they are left as it is. So they archived into single file.
Uses
1. Ease of using in setting classpath
2. Security can be defined so that illegal entities can't use it jarsigning
3. Few applications uses multiple jar files therfore versioning and collaboration will be easy

Answer 2

Thank you for your answer!, but can you give me a little example from a real case for if i meet this concept