下面通过一个例子来说明，这个例子包括2个java文件和一个mf文件:
  
  文件1：Frame1.java
  
  package testjar;
  
  import java.awt.*;
  import java.awt.event.*;
  import javax.swing.*;
  
  public class Frame1 extends JFrame {
   JPanel contentPane;
   BorderLayout borderLayout1 = new BorderLayout();
  
   //Construct the frame
   public Frame1() {
   enableEvents(AWTEvent.WINDOW_EVENT_MASK);
   try {
   jbInit();
   }
   catch(Exception e) {
   e.printStackTrace();
   }
   }
  
   //Component initialization
   private void jbInit() throws Exception {
   contentPane = (JPanel) this.getContentPane();
   contentPane.setLayout(borderLayout1);
   this.setSize(new Dimension(400, 300));
   this.setTitle("Frame Title");
   }
  
   //Overridden so we can exit when window is closed
   protected void processWindowEvent(WindowEvent e) {
   super.processWindowEvent(e);
   if (e.getID() == WindowEvent.WINDOW_CLOSING) {
   System.exit(0);
   }
   }
  }
  
  文件2：App.java
  
  package testjar;
  
  import javax.swing.UIManager;
  import java.awt.*;
  
  public class App {
   boolean packFrame = false;
  
   //Construct the application
   public App() {
   Frame1 frame = new Frame1();
   //Validate frames that have preset sizes
   //Pack frames that have useful preferred size info, e.g. from their layout
   if (packFrame) {
   frame.pack();
   }
   else {
   frame.validate();
   }
   //Center the window
   Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
   Dimension frameSize = frame.getSize();
   if (frameSize.height > screenSize.height) {
   frameSize.height = screenSize.height;
   }
   if (frameSize.width > screenSize.width) {
   frameSize.width = screenSize.width;
   }
   frame.setLocation((screenSize.width - frameSize.width) / 2, (screenSize.height - frameSize.height) / 2);
   frame.setVisible(true);
   }
  
   //Main method
   public static void main(String[] args) {
   try {
   UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
   }
   catch(Exception e) {
   e.printStackTrace();
   }
   new App();
   }
  }
  
  文件3：manif.mf
  
  Main-Class: testjar.App
  
  复制上述的三个文件到一个目录中，用命令行进入这个目录并执行 javac -d . *.java，此时会编译生成class文件，然后执行 jar -cvfm te.jar manif.mf testjar，应该回生成一个名为te.jar的jar文件，双击它，就可以看到效果了！