A JAR (Java ARchive) file is a package file format commonly used to aggregate many Java class files, associated metadata, and resources (text, images, etc.) into one file for distribution.

KEY POINTS ABOUT JAR FILE

1. Purpose

JAR files are used to distribute Java applications and libraries. They bundle multiple files into a single archive, making it easier to deploy and manage Java software.

2. Format

JAR files use the ZIP file format for compression and packaging. This allows them to be compressed, reducing file size and making them more efficient to distribute.

3. Structure

• Manifest File: A special file named META-INF/MANIFEST.MF within the JAR contains metadata about the contents, such as the main class to be executed and versioning information.
• Directories and Files: The JAR can contain directories and files in a hierarchical manner, similar to a ZIP file. This includes compiled .class files, resource files, and other necessary components.

4. Advantages

• Convenience: Bundling all files into one archive simplifies distribution and deployment.
• Efficiency: Compression reduces the size of the files, making them easier and faster to transfer.
• Security: JAR files can be signed to ensure authenticity and integrity, providing security for distributed Java applications.

JAR files are a fundamental part of Java programming, facilitating the distribution and deployment of Java applications and libraries in a standardised and efficient manner.

HOW TO CREATE A JAR FILE ?

1. Compile Your Java Code

Compile your .java files into .class files using javac. For example:

javac -d <dir> src/com/example/MyClass.java