求教,读取ZIP包中TEXT或JAVA文件,但老出现空指针异常!!!

Question

import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.util.*;
import java.util.zip.*;
import javax.swing.*;
import javax.swing.filechooser.FileFilter;public class ZipTest
{
public static void main(String[] args)
{
ZipTestFrame frame = new ZipTestFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
class ZipTestFrame extends JFrame
{
public ZipTestFrame()
{
setTitle("zip"); JMenuBar menuBar = new JMenuBar();
JMenu menu = new JMenu("File");
JMenuItem openItem = new JMenuItem("open");
menu.add(openItem);
openItem.addActionListener(new OpenAction());

JMenuItem exitItem = new JMenuItem ("Exit");
menu.add(exitItem);
exitItem.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent event)
{
System.exit(0);
}
});
menuBar.add(menu);
setJMenuBar(menuBar);
JTextArea fileText = new JTextArea();
final JComboBox fileCombo = new JComboBox();
fileCombo.addActionListener(new ActionListener()
{
/**
这里没有实例化OpenAction这个类,是如果调用到的loadZipFile这个方法的?
*/
public void actionPerformed(ActionEvent event)
{
OpenAction open = new OpenAction();
open.loadZipFile((String)fileCombo.getSelectedItem());
}
}

);
getContentPane().add(fileCombo,BorderLayout.SOUTH);
getContentPane().add(new JScrollPane(fileText),BorderLayout.CENTER);

}

private  class OpenAction implements ActionListener
{

public void actionPerformed(ActionEvent event)
{
JFileChooser chooser = new JFileChooser();
chooser.setCurrentDirectory(new File("."));
ExtensionFileFilter filter=new ExtensionFileFilter();
filter.addExtension(".zip");
filter.addExtension(".jar");
filter.setDescription("ZIP archives");
chooser.setFileFilter(filter);
int r=chooser.showOpenDialog(ZipTestFrame.this);
if (r == JFileChooser.APPROVE_OPTION)
{
zipname = chooser.getSelectedFile().getPath();
scanZipFile();
}
} public void scanZipFile()
{
 fileCombo.removeAllItems();
 try
{
 ZipInputStream zin = new ZipInputStream(new FileInputStream(zipname));
 ZipEntry entry;
 while ((entry = zin.getNextEntry())!=null)
 {
 fileCombo.addItem(entry.getName());
 zin.closeEntry();
 }
 zin.close();
 }
 catch(IOException e)

 {
  e.printStackTrace();  
}
}
public  void loadZipFile(String name)
{
    try
{
ZipInputStream zin = new ZipInputStream(new FileInputStream(zipname));
ZipEntry entry;
fileText.setText("");
while((entry = zin.getNextEntry())!=null)
{
if (entry.getName().equals(name))
{
BufferedReader in=new BufferedReader(new InputStreamReader(zin));
String line;
while ((line = in.readLine())!=null)
{
fileText.append(line);
fileText.append("\n");
}
}
zin.closeEntry();
}
zin.close();
}
catch(IOException e)
{
e.printStackTrace();
}
} public static final int DEFAULT_WIDTH = 400;
public static final int DEFAULT_HEIGHT = 300;

private JComboBox fileCombo;
private JTextArea fileText;
private String zipname;}class ExtensionFileFilter extends FileFilter
{ public void addExtension(String extension)
{
if (!extension.startsWith("."))
{
extension="."+extension;
extensions.add(extension.toLowerCase());
}
} public void setDescription(String aDescription)
{
description = aDescription;
} public String getDescription()
{
return description;
} public boolean accept(File f)
{
if (f.isDirectory())
{
return true;
}
return true;
}

private String description="";
private ArrayList extensions=new ArrayList();
}}
请指教

Answer 1

你的内部类中的fileCombo成员变量没有实例化

Answer 2

public void scanZipFile()这个方法在调用fileCombo.removeAllItems();前先实例化一下fileCombo
fileCombo = new JComboBox() ;

Answer 3

提示空指针是在86行,也就是在初始化文件时候说的fileCombo异常空
还没到调用fileCombo的监听啊
所以我感觉应该不是内部类的问题吧

Answer 4

scanZipFile()中确实没有实力化fileCombo
但我实力化了还不对你改个完整的给我行不,kevinliuu

Answer 5

差不多OK了
问题在于,如何把,初始化的fileCombo,传入到scanZipFile()
 但现在初始化的fileCombo定义为 final

Answer 6

import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.util.*;
import java.util.zip.*;
import javax.swing.*;
import javax.swing.filechooser.FileFilter;public class ZipTest
{
    public static void main(String[] args)
    {
        ZipTestFrame frame = new ZipTestFrame();
        frame.setSize(400, 300);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
}
class ZipTestFrame extends JFrame
{
     private final static JComboBox fileCombo = new JComboBox();
     private static JTextArea fileText = new JTextArea();
     private static String zipname;
//    JComboBox fileCombo ;//= new JComboBox();
    public ZipTestFrame()
    {
        setTitle("zip");        JMenuBar menuBar = new JMenuBar();
        JMenu menu = new JMenu("File");
        JMenuItem openItem = new JMenuItem("open");
        menu.add(openItem);
        openItem.addActionListener(new OpenAction());        JMenuItem exitItem = new JMenuItem("Exit");
        menu.add(exitItem);
        exitItem.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent event)
            {
                System.exit(0);
            }
        });
        menuBar.add(menu);
        setJMenuBar(menuBar);
        
       
        fileCombo.addActionListener(new ActionListener()
        {
            /**
             这里没有实例化OpenAction这个类,是如果调用到的loadZipFile这个方法的?
             */
            public void actionPerformed(ActionEvent event)
            {
                OpenAction open = new OpenAction();
                open.loadZipFile((String) fileCombo.getSelectedItem());
            }
        }        );
        getContentPane().add(fileCombo, BorderLayout.SOUTH);
        getContentPane().add(new JScrollPane(fileText), BorderLayout.CENTER);    }    private class OpenAction implements ActionListener
    {
        public void actionPerformed(ActionEvent event)
        {
            JFileChooser chooser = new JFileChooser();
            chooser.setCurrentDirectory(new File("."));
            ExtensionFileFilter filter = new ExtensionFileFilter();
            filter.addExtension(".zip");
            filter.addExtension(".jar");
            filter.setDescription("ZIP archives");
            chooser.setFileFilter(filter);
            int r = chooser.showOpenDialog(ZipTestFrame.this);
            if (r == JFileChooser.APPROVE_OPTION)
            {
                zipname = chooser.getSelectedFile().getPath();
                scanZipFile();
            }
        }        public void scanZipFile()
        {
            ZipTestFrame.fileCombo.removeAllItems();
            try
            {
                ZipInputStream zin = new ZipInputStream(new FileInputStream(
                    zipname));
                ZipEntry entry;
                while ((entry = zin.getNextEntry()) != null)
                {
                    fileCombo.addItem(entry.getName());
                    zin.closeEntry();
                }
                zin.close();
            }
            catch (IOException e)            {
                e.printStackTrace();
            }
        }
        public void loadZipFile(String name)
        {
            try
            {
                ZipInputStream zin = new ZipInputStream(new FileInputStream(zipname));
                ZipEntry entry;
                ZipTestFrame.fileText.setText("");
                while ((entry = zin.getNextEntry()) != null)
                {
                    if (entry.getName().equals(name))
                    {
                        BufferedReader in = new BufferedReader(new
                            InputStreamReader(zin));
                        String line;
                        while ((line = in.readLine()) != null)
                        {
                            fileText.append(line);
                            fileText.append("\n");
                        }
                    }
                    zin.closeEntry();
                }
                zin.close();
            }
            catch (IOException e)
            {
                e.printStackTrace();
            }
        }        public static final int DEFAULT_WIDTH = 400;
        public static final int DEFAULT_HEIGHT = 300;        //private JComboBox fileCombo= new JComboBox();
       // private JTextArea fileText;
        //private String zipname;    }
    class ExtensionFileFilter extends FileFilter
    {        public void addExtension(String extension)
        {
            if (!extension.startsWith("."))
            {
                extension = "." + extension;
                extensions.add(extension.toLowerCase());
            }
        }        public void setDescription(String aDescription)
        {
            description = aDescription;
        }        public String getDescription()
        {
            return description;
        }        public boolean accept(File f)
        {
            if (f.isDirectory())
            {
                return true;
            }
            return true;
        }        private String description = "";
        private ArrayList extensions = new ArrayList();
    }
}