JAR - Java Archive File is a file that is used by JRE. JRE is also known as Java Runtime Environment. You can use this program to view different JAVA programs as well. One thing about JAR files is that they may contain .CLASS files, and even application resources. This type of file opens using ZIP compressions. You will also be able to use this type of format to create jar tools and you can access them using many different options and selections. There are also many different mobile games that support this type of format also. Mozilla Fire Fox and even SeaMonkey are a couple of java-enabled devices which you can use JAR files. You can store different themes and add ons as well. You may also be aware of Java Virtual Machine which is another name for JRE. They were created under the same developer. If you use different Java programs a lot, then you should consider taking advantage of JAR when you can because it is worth having on your system.