How to view the source code inside a JAR file?

Question

I downloaded the code for a LAN messenger from sourceforge. It is an executable JAR file.
You double-click it and your messenger starts.

I want to study the source code. How do I do that?

Answer 1

Sourceforge has links to the source.

Answer 2

Extract source code from .jar file

(1)Use JD GUI (http://jd.benow.ca/). Open the application, drag and drop your JAR file into it.

(2)You can extract a jar file with the command :

jar xf filename.jar

References : Oracle's JAR documentation