What is a JAR file?
JAR — Java archive
What is it?
A JAR bundles a complete Java application — compiled code, images, configuration files — into a single file that runs directly.
It is, once again, a ZIP archive at heart, supplemented with a manifest that tells the Java virtual machine where to start.
History & origin
The format appeared in 1996 alongside Java, aimed at solving a concrete problem: distributing an application made up of hundreds of files without scattering them.
Its underlying principle has stayed the same for nearly thirty years, and it still powers a substantial share of enterprise software.
Why it is useful
An entire application in a single file, launchable anywhere Java is installed.
It can be signed to guarantee its origin.
Limits & drawbacks
It requires a Java environment installed on the machine.
A JAR from an unknown source is still executable code: caution is warranted.
Practical tips
To inspect the contents of a JAR, convert it to ZIP: you'll see its internal structure.
Never run a JAR downloaded from a dubious source — it's a program, not a document.
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