Common Examples
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Let's say I have a Java application consisting of three 
source files that I wish to distribute:

One.javaTwo.javaThree.java

I also want to call my JAR file example.jar. To make a JAR 
file with just One.java:

   jar CF example.jar One.java
To make a file with all three files listed separately:

   jar CF example.jar One.java Two.java Three.java
To make a file with all three files using a pattern match:

   jar CF example.jar *.java

It goes (almost) without saying that the source files are 
in the same directory you are running the jar command in.



 

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Compress Files To An Executable Java Archive (JAR)
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It is also possible to make an archive that can be executed 
(run) by Java and even by a double click through your OS, 
if you have it set up correctly. Of course, to do this you 
must store compiled class files in the archive, as well as 
or instead of Java source files, since Java source files 
cannot be run! 

Continuing the example above, I now compile my Java source 
files:

   javac *Java
or

   javac One.java Two.java Three.java


 

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Create An Executable JAR
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All JAR files contain something called a manifest file 
which holds information Java wants to know. One piece of 
information a manifest file may contain is the name of a 
class that will be run if the JAR file is executed.

The first thing you must do is create a text file that 
lists the "main" class - the class that has the main method 
you want executed when the JAR is executed. Let's say that 
Three from the above example has the main method I want 
executed. I create a text file called "mainClass.txt" with 
the following text:

Main-Class: Three
 
IMPORTANT: the text file only needs the one line of text 
for this purpose. However, the file must end with a blank 
line or this will not work, ie the file has two lines in 
it - the second one is empty. Note too the class is 
called "Three" and not "Three.java" (the file containing 
the source code) or "Three.class" (the file containing the 
byte codes). If your class file is in a package hierarchy, 
you must use the fully qualified name of the class 
(eg "myPackage.MyClass").

I then run the jar utility with this command line: 

   jar cmf mainClass.txt example.jar *.class
With this line, I told jar to create a JAR file (option c) 
with modifications to the manifest file (option m) as 
specified within mainClass.txt, naming the JAR file (option 
f) as example.jar and including everything that matches the 
pattern *Class



 

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Running An Executable JAR From Command Line
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I can run it from the command line like this:

   java -jar example.jar



 

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Running An Executable JAR From Explorer (Windows)
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Within Windows, it is also possible to set up Windows 
Explorer so that you can double click on the JAR file icon 
to execute the file (handy for GUI applications). The first 
thing you must do is set up the correct association with 
the 'javaw.exe' application that JDK for Windows will have. 
Click here for an older example with pictures! Open Windows 
Explorer and select Tools | Folder Options | File Types.

If there is no JAR file type, create it. Give it a 
description like 

   jar - Executable Jar File
to ensure it sorts under 'jar'. Create or edit the action 
called "open" and associate it with the following action: 

   "C:\Java\jdk1.4.0\bin\javaw.exe" -jar "%1"
Of course, you will replace "C:\Java\jdk1.4.0
\bin\javaw.exe" with whatever path is correct on your 
machine.

IMPORTANT: include the double quotes to take care of names 
with spaces.

If you are using something other than Windows and you know 
how to set up an association in your OS, please contact me.