Does anyone explain what is .jar?

Answer 1

.jar files Java run file for example Windows run file .exe
or jar files contains compiled files and we can use it for library

Answer 2

. jar is extension for compiled java program, which can be run on any computer, which has installed JVM. (Behave like files with extension .exe)

Answer 3

also .jar is a container you still can open it with e.g. 7zip. you will find your compiled class files in there and a manifest file