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！