How to create a executable Jar

Some Java applications are distributed as Jar files, where the user can just double-click the file and 'Bang!' the application opens up. When you double click on a normal Jar file we just get a error message saying "Failed to load Main-Class...".

 

Follow the following steps to create an executable Jar:

 

- Create a simple Swing program which displays a label

 

view plainprint?

1. import javax.swing.*;  
2. import javax.swing.event.*;  
3.   
4. public class HelloWorldSwing {  
5.     /** 
6.      * Create the GUI and show it.  For thread safety, 
7.      * this method should be invoked from the 
8.      * event-dispatching thread. 
9.      */  
10.     private static void createAndShowGUI() {  
11.         //Make sure we have nice window decorations.  
12.         JFrame.setDefaultLookAndFeelDecorated(true);  
13.   
14.         //Create and set up the window.  
15.         JFrame frame = new JFrame("HelloWorldSwing");  
16.         frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  
17.         //Add the ubiquitous "Hello World" label.  
18.         JLabel label = new JLabel("Hello World");  
19.         frame.getContentPane().add(label);  
20.   
21.         //Display the window.  
22.         frame.pack();  
23.         frame.setVisible(true);  
24.     }  
25.   
26.     public static void main(String[] args) {  
27.         //Schedule a job for the event-dispatching thread:  
28.         //creating and showing this application's GUI.  
29.         javax.swing.SwingUtilities.invokeLater(new Runnable() {  
30.             public void run() {  
31.                 createAndShowGUI();  
32.             }  
33.         });  
34.     }  
35. }  

import javax.swing.*;
import javax.swing.event.*;

public class HelloWorldSwing {
    /**
     * Create the GUI and show it.  For thread safety,
     * this method should be invoked from the
     * event-dispatching thread.
     */
    private static void createAndShowGUI() {
        //Make sure we have nice window decorations.
        JFrame.setDefaultLookAndFeelDecorated(true);

        //Create and set up the window.
        JFrame frame = new JFrame("HelloWorldSwing");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        //Add the ubiquitous "Hello World" label.
        JLabel label = new JLabel("Hello World");
        frame.getContentPane().add(label);

        //Display the window.
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        //Schedule a job for the event-dispatching thread:
        //creating and showing this application's GUI.
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }
}

 

- Compile and run it and ensure that it works properly

- Create a file called "mainClass" with the following content in the same directory where you have the class file - if you have put the class inside a package create the file at the root of the package

    Main-Class: HelloWorldSwing

 

    Note the empty new line after the class name.

- From the directory run the following command from the command prompt to create a Jar file - "jar cmf mainClass HelloWorldSwing.jar *.class". This creates the executable Jar file. Here "m" refers to the manifest file - "mainClass"

- Now double click on the Jar file and see your swing application come to life!!