Intoduction to JAR,EAR and WAR files in java

JAR is java arcihve file.It contain all class file,image,sound and other files which will needed in whole application. Computer users can create or extract JAR files using the jar command that comes with the JDK. They can also use zip tools. The JavaTM Archive (JAR) file format enables you to bundle multiple files into a single archive file. jar was designed mainly to facilitate the packaging of java applets or applications into a single archive.

jar cf jar-file input-file(s)

The options and arguments used in this command are:
• Use c option  to create a JAR file.
• jar-file is the name of your  JAR file. You can use any filename for a JAR file. By convention, JAR filenames are given a .jar extension,it is mandatory any way.

The command for viewing the contents of a JAR file is:

jar tf jar-file
An Example
Let’s use the Jar tool to list the contents of the vinay.jar file we created in the previous section:
jar tf vinay.jar
EAR -An Enterprise Archive file represents a J2EE application that can be deployed in a Web Sphere application server. EAR files are standard Java archive files and have the file extension .ear. EAR file contain ejb, web or application client module. ear file is complete j2ee application file that contain all(jar +war)
WAR -Web Archive (WAR) file is a Java archive file used to store jsp,servlets,classes,meta data information,images and
Sound and tag libararies etc. Its standard file extension is .war. WAR files are used to package Web modules. A WAR file is for a Web application deployed to a servlet/jsp engine.

In shot we can say
EAR = WAR(Web module) + JAR(can be EJB module or application client module)

for more information check this one -http://java.sun.com/docs/books/tutorial/deployment/jar/build.html