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November 2001



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Need help with FileFilter

Posted by Thi on November 28, 2001 at 3:15 PM


I would like to restrict files shown in a file dialog. I've tried to do this by implementing the FileFilter interface, exactly shown in the Core Java book in Chapter 9 under File Dialogs. However, I'm getting an error stating that FileFilter must be an interface. Can someone look at my code and tell me what I have done wrong? Or, can someone show me another way to filter files? Here is my code, which creates a Frame that contains two buttons--one for an open dialog box and the other for a save dialog box:

import java.util.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.filechooser.*;
import javax.swing.filechooser.FileFilter;

public class FileChooserDemo extends JFrame {
static private final String newline = "\n";

//This is where the compiler says FileFilter must be an
class TxtFilter implements javax.swing.filechooser.FileFilter
public boolean accept(File f)
return f.getName().toLowerCase().endsWith(".txt") || f.isDirectory();

public String getDescription()
return "Text file";

public FileChooserDemo() {

//Create the log first, because the action listeners
//need to refer to it.
final JTextArea log = new JTextArea(5,20);
log.setMargin(new Insets(5,5,5,5));
JScrollPane logScrollPane = new JScrollPane(log);

//Create a file chooser
final JFileChooser fc = new JFileChooser();
fc.setCurrentDirectory(new File("."));
fc.setFileFilter(new TxtFilter()); //sets the filter to .txt files

//Create the open button
JButton openButton = new JButton("Open a File...");
openButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
int returnVal = fc.showOpenDialog(FileChooserDemo.this);

if (returnVal == JFileChooser.APPROVE_OPTION) {
File file = fc.getSelectedFile();
//this is where a real application would open the file.

log.append("Opening: " + file.getName() + "." + newline);
} else {
log.append("Open command cancelled by user." + newline);

//Create the save button
JButton saveButton = new JButton("Save a File...");
saveButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
int returnVal = fc.showSaveDialog(FileChooserDemo.this);

if (returnVal == JFileChooser.APPROVE_OPTION) {
File file = fc.getSelectedFile();

//this is where a real application would save the file.
//export the range of events as a .cal file, which can be imported
String filename = file.getName();

log.append("Saving: " + file.getName() + "." + newline);
} else {
log.append("Save command cancelled by user." + newline);

//For layout purposes, put the buttons in a separate panel
JPanel buttonPanel = new JPanel();

//Explicitly set the focus sequence.

//Add the buttons and the log to the frame
Container contentPane = getContentPane();
contentPane.add(buttonPanel, BorderLayout.NORTH);
contentPane.add(logScrollPane, BorderLayout.CENTER);

public static void main(String[] args) {

JFrame frame = new FileChooserDemo();

frame.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {



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