JAR is short for Java Archive. It is a file very similar to ZIP files, a file structure that compresses and contains other files. A Jar file includes meta information about the files in its MANIFEST file as well as checksums. In the JDK1.2, you can create an executable Jar file by just specifying the class where the main program entry point inside the MANIFEST file. The JDK tool jarsigner allows you to digitally sign a Jar file and verify it to ensure it didn't change since it was signed.
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