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What is a JAR file?
A JAR file is an archive saved in the Java archive (JAR) format, which utilizes Zip-compression. It is typically used as a program library or as a standalone program that runs if Java Runtime Environment (JRE), a framework used for executing Java programs, is installed on the computer or mobile device.
JAR files contain CLASS files, application resources, and an optional manifest file (META-INF/MANIFEST.MF). They are compressed using .ZIP compression and may optionally be digitally signed using the jarsigner tool included with the Java SDK. JAR files may be created with the jar tool, and they can be accessed using Java's java.util.jar API.
JAR files are used for some mobile games supported by Java-enabled mobile devices. They are also used by Mozilla Firefox, Thunderbird, SeaMonkey, and Sunbird to store themes and add-ons.
NOTE: The Java Runtime Environment is also referred to as the Java Virtual Machine (JVM). Sun Microsystems, the original developers of the JRE/JVM, were acquired by Oracle.
How to open a JAR file
JAR files are typically used to distribute applications that can be run with the Oracle Java Runtime Environment (multiplatform). If you have JRE installed and set as the default program associated with JAR files, you can simply double-click the JAR file to run it. When you do this on a Mac, Apple Jar Launcher (bundled with macOS) passes the JAR file to JRE, or JVM, which runs the file.
You can also view, extract, run, and create JAR files with the Java Archive Tool provided as part of the Java Development Kit (JDK) included in the Oracle Java SE Development Kit. The Java Archive Tool is a command-line utility and here are the commands associated with the different capabilities:
- To view a JAR file - jar tf jar file
- To extract a JAR file - jar xf jar file
- To run a JAR file - java -jar app.jar
- To create a JAR file - jar cf jar file input file(s)
NOTE: If you are looking to extract the contents from a JAR file, you can use various decompression utilities, such as Corel WinZip (Windows), Corel WinZip Mac (Mac), RARLAB WinRAR (Windows), and 7-Zip (Windows).