How to view the contents of a jar file.
Command

// From the cmd line
jar -tvf fileName.jar

Example Output

C:\BrowserGUI\dist>jar -tvf BrowserGUI.jar
     0 Sat Nov 26 21:46:28 PST 2011 META-INF/
   106 Sat Nov 26 21:46:26 PST 2011 META-INF/MANIFEST.MF
 39313 Sat Nov 26 21:46:26 PST 2011 GUIAboutTab.class
 39952 Sat Nov 26 21:46:26 PST 2011 GUIFrame.class
 45354 Sat Nov 26 21:46:26 PST 2011 GUITabbedPane.class
  5244 Sat Nov 26 21:46:26 PST 2011 GUImain.class
   691 Sat Nov 26 21:46:26 PST 2011 NewJFrame$1.class
   509 Sat Nov 26 21:46:26 PST 2011 NewJFrame$2.class
 15458 Sat Nov 26 21:46:26 PST 2011 NewJFrame.class

Check out the Java Package Tutorial for more infomation.