下图是Applet查看器运行下列Java Applet点击“显示系统时间”按的显示内容,请根据程序注释要求补充完整程序。程序代码如下: package showtimesample; import java.awt.*; import java.awt.event.*; import javax.swing.*; import java.util.*; import java.text.*; public class ShowTimeSample extends JApplet { private static final long serialVersionUID = 1L; FlowLayout flowLayout = new FlowLayout(); JButton jButton = new JButton(); JTextField jTextField = new JTextField(); public void init() { try { showInit(); }catch (Exception e) { e.printStackTrace(); } } private void showInit() throws Exception { this.setSize(120, 80); jButton.setText("显示系统时间"); this.getContentPane().setLayout(flowLayout); this.getContentPane().add(jButton); jButton.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { jButton_actionPerformed(e); } }); this.getContentPane().add(jTextField); jTextField.setText("系统时间"); } public void jButton_actionPerformed(ActionEvent e) { //取得系统当前时间。 Date timenow =___________________; SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日 hh:mm:ss a"); String s_time_msg = sdf.format(timenow); int l = s_time_msg.length()*8; jTextField.setSize(l,jTextField.getHeight()); //将系统当前时间字符串显示在文本框内。 jTextField.setText(_______________); } }