这是为什么呢?..........请大家帮忙来看一下!(顺便问一下如何个别人加分呢?

下面的程序能够编译通过,但在浏览器中不能显示,用了其他的浏览器同样结果,同时我也装了JDK PLUG-IN1.4,(其中只要遇到利用ImageIcon对象的便不能显示,用其他的SWING中的对象能正确显示,)请问如何让ImageIcon在浏览器中显示呢?
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Test extends JApplet {
private JTabbedPane tp = new JTabbedPane(SwingConstants.BOTTOM);
private JComboBox combo = new JComboBox();

public Test() {
Container contentPane = getContentPane();
JPanel comboPanel = new JPanel();
JPanel panelOne = new JPanel();
JPanel panelTwo = new JPanel();

tp.add(panelOne, "Panel One");
tp.addTab("Panel Two", new ImageIcon(getDocumentBase(),"document.gif"),panelTwo, "tooltip text");

combo.addItem("TOP");
combo.addItem("LEFT");
combo.addItem("RIGHT");
combo.addItem("BOTTOM");

setComboValue();

comboPanel.add(new JLabel("Tab Placement:"));
comboPanel.add(combo);

contentPane.setLayout(new BorderLayout());
contentPane.add(comboPanel, BorderLayout.NORTH);
contentPane.add(tp, BorderLayout.CENTER);

combo.addItemListener(new ItemListener() {
public void itemStateChanged(ItemEvent e) {
JComboBox cb = (JComboBox)e.getSource();
int state = e.getStateChange();

if(state == ItemEvent.SELECTED) {
String s = (String)cb.getSelectedItem();

if(s.equals("TOP"))
tp.setTabPlacement(JTabbedPane.TOP);
else if(s.equals("LEFT"))
tp.setTabPlacement(JTabbedPane.LEFT);
else if(s.equals("RIGHT"))
tp.setTabPlacement(JTabbedPane.RIGHT);
else if(s.equals("BOTTOM"))
tp.setTabPlacement(JTabbedPane.BOTTOM);
tp.validate();
}
}
});
}
private void setComboValue() {
int placement = tp.getTabPlacement();
String selectedItem = null;

switch(placement) {
case JTabbedPane.TOP:
selectedItem = "TOP";
break;
case JTabbedPane.LEFT:
selectedItem = "LEFT";
break;
case JTabbedPane.RIGHT:
selectedItem = "RIGHT";
break;
case JTabbedPane.BOTTOM:
selectedItem = "BOTTOM";
break;
}
combo.setSelectedItem(selectedItem);
}
}