What is rt.jar in Java/Jdk/Jre???

rt.jar = Run Time Jar file.

It provides all the essential APIs to your application during runtime. In this case it doesn't matter that whether you have jdk installed on your machine or not. If you have Jre on your system so your application will execute and collect all APIs from rt.jar.

Some tend to think it stands for RooT, since this jar contains all java build-in classes. But I have yet to find any official Sun documents regarding this acronym.

Q: What does jar stand for? Jar stands for Java Archive. A jar file usually has file name extension .jar. It contains mainly java class files but any types of files can be included, e.g., XML files, HTML files, properties files, gif/jpg image files, text files, PDF files, and binary files, and so on.

Q: What is the difference between a jar file and a zip file? Basically, a jar file is the same as a zip file, except that the jar file contains a META-INF directory to store metadata or attributes. The most well-known file is META-INF/MANIFEST.MF. You can customize the content of a MANIFEST.MF when creating a jar file, and if you don't, a default one is generated and included. For example:

Manifest-Version: 1.0
Created-By: 1.5.0_06 (Sun Microsystems Inc.)

It's perfectly fine to have other configuration files and directories under META-INF.

Posted by:
Abhishek Chitransh (Technology Consultant)