一个简单的问题

我现在给你一个打开文件的演示程序，看不能给你点帮助。
import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import java.beans.*;
import java.util.*;
import java.io.*;
import javax.swing.*;
import javax.swing.filechooser.FileFilter;
import javax.swing.filechooser.FileView;
public class FileChooserTest
{
public static void main(String args[])
{
FileChooserFrame frame=new FileChooserFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
frame.setResizable(false);
}
}
class FileChooserFrame extends JFrame
{
public FileChooserFrame()
{
setTitle("FileChooserTest");
setSize(WIDTH,HEIGHT);

//set up menu bar
JMenuBar mbar=new JMenuBar();
setJMenuBar(mbar);
JMenu menu=new JMenu("File");
mbar.add(menu);

JMenuItem mItem=new JMenuItem("Open");
menu.add(mItem);
mItem.addActionListener(new FileOpenListener());
JMenuItem exitItem=new JMenuItem("Exit");
menu.add(exitItem);
exitItem.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent event)
{
System.exit(0);
}
});
//uses a label display the images
label=new JLabel();
Container con=getContentPane();
con.add(label);

chooser =new JFileChooser();
}

private class FileOpenListener implements ActionListener
{
public void actionPerformed(ActionEvent event)
{
//set up file chooser
chooser.setCurrentDirectory(new File("."));
//accept all images files ending with .jpg,.jpeg,.gif
final ExtensionFileFilter filter=new ExtensionFileFilter();
filter.addExtension("jpg");
filter.addExtension("jpeg");
filter.addExtension("gif");
filter.setDescription("Image files");
chooser.setFileFilter(filter);

chooser.setAccessory(new ImagePreviewer(chooser));

//show file chooser dialog
int result=chooser.showOpenDialog(FileChooserFrame.this);
//if  image file accepted ,set it as icon of the label
if(result==JFileChooser.APPROVE_OPTION)
{
String name=chooser.getSelectedFile().getPath();
label.setIcon(new ImageIcon(name));
}
}
}
public static final int WIDTH=300;
public static final int HEIGHT=400;

private JLabel label;
private JFileChooser chooser;
}
/**
this file filter matches all files  with  a given set of extension
*/
class ExtensionFileFilter extends FileFilter
{
/**
adds an extension that this file filter recognize
@param extension a file extension(such as ".txt" or "txt")
*/
public void addExtension(String extension)
{
if(!extension.startsWith("."))
extension="."+extension;
extensions.add(extension.toLowerCase());
}
/**
sets a description for the file set that this file filter recognize
@param aDescriprtion a description for file set
*/
public void setDescription(String aDescription)
{
description=aDescription;
}
/**
returns a description for the file set that this file filter recognizes
@return a description for file set
*/
public String getDescription()
{
return description;
}
public boolean accept(File f)
{
if(f.isDirectory()) return true;
String name =f.getName().toLowerCase();

//check if the file name ends with any of the extensions
for(int i=0;i<extensions.size();i++)

   if(name.endsWith((String)extensions.get(i)))
  return true;

      return false;

}
private  String description="";
private ArrayList extensions=new ArrayList();
}
/** a file view that display an icon for all files that match a file filter
*/
class FileIconView extends FileView
{
/**
constructs a fileIconView
@param aFilter a file filter--all files that this filter
  accepts will be shown with the icon
  @param anIcon--the icon shown with all accepted files
*/
public FileIconView(FileFilter aFilter,Icon anIcon)
{
filter=aFilter;
icon=anIcon;
}
public Icon getIcon(File f)
{
if(!f.isDirectory()&& filter.accept(f))
return icon;
else return null;
}
private FileFilter filter;
private Icon icon;
}
/**
a file chooser accessory that  preview images
*/
class ImagePreviewer extends JLabel
{
/**
constructs an ImagePreviewer
@param chooser the file chooser whose property changes
trigger an image change in this previewer
*/
public ImagePreviewer(JFileChooser chooser)
{
setPreferredSize(new Dimension(100,100));
setBorder(BorderFactory.createEtchedBorder());

chooser.addPropertyChangeListener(new PropertyChangeListener()
{
public void propertyChange(PropertyChangeEvent event)
{
if(event.getPropertyName()==JFileChooser.SELECTED_FILE_CHANGED_PROPERTY)
{
File f=(File)event.getNewValue();
ImageIcon icon=new ImageIcon(f.getPath());
if(icon.getIconWidth()>getWidth())
icon=new ImageIcon(icon.getImage().getScaledInstance(getWidth(),-1,Image.SCALE_DEFAULT));
setIcon(icon);
}
}
});
}
}
又来混分：
//: FileDialogTest.java
// Demonstration of File dialog boxes
import java.awt.*;public class FileDialogTest extends Frame {
  TextField filename = new TextField();
  TextField directory = new TextField();
  Button open = new Button("Open");
  Button save = new Button("Save");
  public FileDialogTest() {
    setTitle("File Dialog Test");
    Panel p = new Panel();
    p.setLayout(new FlowLayout());
    p.add(open);
    p.add(save);
    add("South", p);
    directory.setEditable(false);
    filename.setEditable(false);
    p = new Panel();
    p.setLayout(new GridLayout(2,1));
    p.add(filename);
    p.add(directory);
    add("North", p);
  }
  public boolean handleEvent(Event evt) {
    if(evt.id == Event.WINDOW_DESTROY)
      System.exit(0);
    else
      return super.handleEvent(evt);
    return true;
  }
  public boolean action(Event evt, Object arg) {
    if(evt.target.equals(open)) {
      // Two arguments, defaults to open file:
      FileDialog d = new FileDialog(this,
        "What file do you want to open?");
      d.setFile("*.java"); // Filename filter
      d.setDirectory("."); // Current directory
      d.show();
      String openFile;
      if((openFile = d.getFile()) != null) {
        filename.setText(openFile);
        directory.setText(d.getDirectory());
      } else {
        filename.setText("You pressed cancel");
        directory.setText("");
      }
    }
    else if(evt.target.equals(save)) {
      FileDialog d = new FileDialog(this,
        "What file do you want to save?",
        FileDialog.SAVE);
      d.setFile("*.java");
      d.setDirectory(".");
      d.show();
      String saveFile;
      if((saveFile = d.getFile()) != null) {
        filename.setText(saveFile);
        directory.setText(d.getDirectory());
      } else {
        filename.setText("You pressed cancel");
        directory.setText("");
      }
    }
    else
      return super.action(evt, arg);
    return true;
  }
  public static void main(String[] args) {
    Frame f = new FileDialogTest();
    f.resize(250,110);
    f.show();
  }
} ///:~

调试易

一个简单的问题

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