How to create a runnable Jar File

What is a Jar File?

A jar file is a Java Archive File and is built off of the zip format that is familiar to many Windows users. Jar files allow you to compress data to take up less space and they allow you to combine many individual files into one entity. For instance, if you have two compiled classes.

• A.class
• B.class

You could combine both of these classes into one jar file.

Before anything else

We are going to need at least one class to compile into a jar. I will use a class called JarDemo. First, let's compile the JarDemo.java file into a class file. I recommend using the class I've created.

import javax.swing.JOptionPane; 				
public class JarDemo{

public static void main(String[] args){
	String inputValue = JOptionPane.showInputDialog("Type Some Input");
	JOptionPane.showMessageDialog(null, "You input " + inputValue);
	}

}

Step 1: Locate the Jar utility in the JDK folder

• Before you do anything else, make sure that you have jdk installed on your computer. You also will need to know the directory to the jdk. Specifically, you will need the path to the Jar utility that is inside your jdk folder. My path to jar is:

   C:\"Program Files"\Java\jdk1.6.0_02\bin\jar
  

  • As you can probably tell, I'm using Java 1.6 and within the 'bin' folder is jar which is the program that you will use to make jar files. Basically typing that line up above tells the command prompt that we're going to run the jar utility which is located in the folder C:\"Program Files"\Java\jdk1.6.0_02\bin
  • On your own computer, the path to the jar utility will probably look similar, it depends on where you installed the jdk to.

Step 2: Create themanifest file

Since you could potentially be compiling many files into one jar file, Java needs to know which one will have the main method. Our example is a bit more trivial since we're just compiling one class into a Jar. Nonetheless, the way that Java knows which of classes has the main method is from a single line in what's known as a manifest file. A manifest file can be a text file made with notepad. I called my manifest file manifest.txt, my manifest file says:

Main-Class: JarDemo

As you can see themanifest file states that the main-class is JarDemo.
Warning: A subtle yet critical point is that you MUST end the manifest file with an empty new line.

Last Step: Compile The Jar!

1)Use the command prompt to navigate to where the JarDemo.class and manifest.txt file are saved and type :

C:\>  C:\Path\to\jdk\bin\jar cvfm jarDemoCompiled.jar manifest.txt JarDemo.class

If you don't like always typing out the generally long path to the jdk. You can set the path as follows

• c:> path c:\path\to\jdk\bin;%path%

Doing so would allow you to type

C:\>  jar cvfm jarDemoCompiled.jar manifest.txt JarDemo.class

When I don't usde the shortcut on my computer, I must type:

C:\>  C:\"Program Files"\Java\jdk1.6.0_02\bin\jar cvfm jarDemoCompiled.jar manifest.txt JarDemo.class

cvfm means "create a jar; show verbose output; specify the output jar file name (jarDemoCompiled.jar); specify the manifest file name(manifest.txt) and use the file JarDemo.class to create the jar

Here's the actual screen shot from my command prompt. Remember the path to jdk\bin\jar will be similar on your computer but almost definitely not exactly the same as mine.

What if you want to compile all .class files in the folder into the jar?

No problem, instead of the last line up above, type:

C:\>  C:\Path\to\jdk\bin\jar cvfm jarDemoCompiled.jar manifest.txt *.class

Hopefully, at this point you have a picture like I have below in your folder. Just click on the Jar file and your program should run!