ＺＩＰ文件不能读取！！大家帮帮忙！！
在程序运行时有如下信息： 
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException 
at ZipTestFrame.scanZipFile(ZipTest.java:78) 
at ZipTestFrame$OpenAction.actionPerformed(ZipTest.java:70) 
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2013) 
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2336) 
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:405) 
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:260) 
at javax.swing.AbstractButton.doClick(AbstractButton.java:375) 
at javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:1689) 
at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(BasicMenuItemUI.java:1733) 
at java.awt.Component.processMouseEvent(Component.java:6100) 
at javax.swing.JComponent.processMouseEvent(JComponent.java:3288) 
at java.awt.Component.processEvent(Component.java:5865) 
at java.awt.Container.processEvent(Container.java:2110) 
at java.awt.Component.dispatchEventImpl(Component.java:4461) 
at java.awt.Container.dispatchEventImpl(Container.java:2168) 
at java.awt.Component.dispatchEvent(Component.java:4287) 
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4466) 
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4130) 
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4060) 
at java.awt.Container.dispatchEventImpl(Container.java:2154) 
at java.awt.Window.dispatchEventImpl(Window.java:2555) 
at java.awt.Component.dispatchEvent(Component.java:4287) 
at java.awt.EventQueue.dispatchEvent(EventQueue.java:605) 
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:276) 
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:201) 
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:191) 
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:186) 
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:178) 
at java.awt.EventDispatchThread.run(EventDispatchThread.java:139) 
程序如下： 

import java.awt.BorderLayout; 
import java.awt.event.ActionEvent; 
import java.awt.event.ActionListener; 
import java.io.*; 
import java.util.ArrayList; 
import java.util.zip.ZipEntry; 
import java.util.zip.ZipInputStream; 
import javax.swing.*; 
import javax.swing.filechooser.FileFilter; 
public class lianxi { 
public static void main(String[] args) 
{ 
ZipTestFrame f=new ZipTestFrame(); 
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
f.setVisible(true); 
} 
} 
class ZipTestFrame extends JFrame 
{ 
public ZipTestFrame() 
{ 
setTitle("ZipTest"); 
setSize(100,100); 

JMenuBar menuBar=new JMenuBar(); 

  JMenu menu=new JMenu("文件"); 
  JMenuItem menu1=new JMenuItem("打开"); 
  menu1.addActionListener(new OpenAction()); 
  JMenuItem menu2=new JMenuItem("退出"); 
  menu2.addActionListener(new ActionListener() 
  { 
  public void actionPerformed(ActionEvent event){ 
  System.exit(0); 
  } 
  }); 
  menu.add(menu1); 
  menu.add(menu2); 
  menuBar.add(menu); 
  setJMenuBar(menuBar);