Packaging Programs in JAR Files

• Working with JAR files (ref)
  The Java™ Archive (JAR) file format enables you to bundle multiple files into a single archive file. Typically a JAR file contains the class files and auxiliary resources associated with applets and applications.
  JAR files are packaged with the ZIP file format, so you can use them for tasks such as lossless data compression, archiving, decompression, and archive unpacking.
  

  To create a JAR file	jar cf jar-file input-file(s)
  To extract the contents of a JAR file	jar xf jar-file
  To run an application packaged as a JAR file	java -jar app.jar

• Working with manifest files (ref)
  JAR files support a wide range of functionality, including electronic signing, version control, package sealing, and others. What gives a JAR file this versatility? The answer is the JAR file's manifest.
  The manifest is a special file that can contain information about the files packaged in a JAR file. When you create a JAR file, a default manifest is created automatically. By tailoring this "meta" information that the manifest contains, you enable the JAR file to serve a variety of purposes: for example, the manifest file tells the application's entry point with the Main-Class header.
  

Using Eclipse to create JAR files

• Fairly easy. Once programs are written up and compiled (run), use export function to export a jar package.
  Export -> Java -> Runnable JAR file
  
• But if you want to create a Jar file with source files as well,
  Export -> Java -> JAR file ->->-> (just follow the steps)
  
  • When you specify the jar file, make sure you check "Export Java source files and resources"
  • When you do the JAR Manifest Specification, you can choose to use existing manifest file, or let Eclipse generate the manifest file (forthe latter, make sure you select the class of the application entry point!)

Creating JAR files using command lines in linux

• Compile the codes
  javac huffman/*.java
  
• Create a manifest folder (META-INF) and create a manifest file (MANIFEST.MF) under that folder.
  Here is the manifest file:
  

  Manifest-Version: 1.0
  Main-Class: huffman.HuffCode
  

• Create a jar file
  

  jar cfm huffcode.jar META-INF/MANIFEST.MF huffman/