Go to file->export->runnable jar and select the class which contains the main
method.
Setting .JAR File Association
Normally, the installation program for the Java 2 Runtime Environment will register a default file association so that .JAR files will execute with 'JAVAW -JAR' by double-clicking any .JAR file. If this does not happen, or it somehow gets changed, then manually setting the association for *.JAR files may be needed.
- Open the Windows Explorer, from the Tools select 'Folder Options...'
- Click the File Types tab, scroll down and select JAR File type.
- Press the Advanced button.
- In the Edit File Type dialog box, select open in Actions box and click Edit...
- Press the Browse button and navigate to the location the Java interpreter javaw.exe.
- In the Application used to perform action field, needs to display something similar to
"C:\Program Files\Java\j2re1.4.2_04\bin\javaw.exe" -jar "%1" %*
then press the OK buttons until all the dialogs are closed.
Now you should be able to launch any *.JAR
program by double-clicking it.
This step by step guid was taken from: http://windowstipoftheday.blogspot.com/2005/10/setting-jar-file-association.html