JAR files are those used for distributing programs written in Java and used by the Java Runtime Environment. When you have JRE installed, JAR (Java Archive) files are run as a standalone program or JAR files can serve as a program library. JAR files can be downloaded by your browser or you may receive a JAR file that requires you to run a Java application.
The JAR file format is both a container and compression format since it compresses and contains other files. This also makes JAR files relatively easy to open, plus there are a variety of programs available which are designed to open files with the file extension JAR.
In terms of content, JAR files can contain files which are used by gaming applications and they are also used to store files and add-ons for Mozilla Firefox, SeaMonkey, and Thunderbird email. A JAR file does not necessarily have to be compressed, but when it is, the Zip compression algorithm is the method used for compressing it.
How to Open JAR Files
JAR files can be opened and viewed using decompression software that is designed to handle ZIP files. Java itself is also capable of opening JAR files and running the software that is contained in the file. Although JAR files are created in a format that is similar to ZIP, there is a reason that JAR files contain a different file extension.
JAR files are created with source code that can make the file an executable, which means it is capable of running a software program. For this reason, there are only two methods you can use to open and use a JAR file aside from using your web browser.
First, you can choose to download and install decompression software such as WinZip for Windows or Apple Jar Launcher for Mac OS X. Then you must change the JAR file extension to ZIP. Once you have installed the decompression software, it will unzip files that have been changed from JAR to ZIP so you can open the folder and view the contents.
If a JAR file is designed as an executable, then you must use the Oracle Java Runtime Environment to open is as a software program. JRE is compatible with all operating systems including Windows, Mac OS X and Linux. If you are unable to open the file in JRE, it means the file is not an executable type of JAR file and you will need to use your browser or decompression software to open and view the file.