How to Open Up a JAR File
A JAR file is the standard container for Java applications. It contains the compiled classes and other data that make up an executable Java program. The JAR file format is based on the ZIP format. You can browse ZIP archives on Windows 8 using built-in features. Since a JAR file is structured as a ZIP file, the simplest way to open it is to change the extension to ".zip."
Rename the File Extension
As an example, assume the target JAR file is named "xyz.jar." Locate the file with File Explorer. Rename "xyz.jar" to "xyz.zip." Tap or double-click on "xyz.zip." This displays the contents of the archive in File Explorer. You can extract individual files by selecting them and dragging them to other folders. You can extract everything in the archive by selecting "Compressed Folder Tools" and then tapping or clicking "Extract All." Change the extension back to ".jar" when you no longer need to view or extract the contents.
Copying the JAR and Renaming the Copy
Since a JAR is an executable file, make a copy of the file and then rename the extension of the copy. The JAR may be in use by running programs. However, if no other program depends on the JAR, it is fine to simply change the extension and change it back.