Class Image Viewer

import java.awt.*;
 import java.awt.event.*;
 import java.awt.image.*;
 import javax.swing.*;
 import java.io.File;

 public class ImageViewer
 {
   // static fields:
   private static final String VERSION = "Version 1.0";
   private static JFileChooser fileChooser = new JFileChooser(System.getProperty("user.dir"));
   // fields:
   private JFrame frame;
   private ImagePanel imagePanel;
   private JLabel filenameLabel;
   private JLabel statusLabel;
   private OFImage currentImage;
   /**
    * Create an ImageViewer show it on screen.
    */
   public ImageViewer()
   {
     currentImage = null;
     makeFrame();
   }
   // ---- implementation of menu functions ----
   /**
    * Open function: open a file chooser to select a new image file.
    */
   private void openFile()
   {
     int returnVal = fileChooser.showOpenDialog(frame);
     if(returnVal != JFileChooser.APPROVE_OPTION) {
       return; // cancelled
     }
     File selectedFile = fileChooser.getSelectedFile();
     currentImage = ImageFileManager.loadImage(selectedFile);
     if(currentImage == null) {  // image file was not a valid image
       JOptionPane.showMessageDialog(frame,
           "The file was not in a recognized image file format.",
           "Image Load Error",
           JOptionPane.ERROR_MESSAGE);
       return;
     }
     imagePanel.setImage(currentImage);
     showFilename(selectedFile.getPath());
     showStatus("File loaded.");
     frame.pack();
   }
   /**
    * Close function: close the current image.
    */
   private void close()
   {
     currentImage = null;
     imagePanel.clearImage();
     showFilename(null);
   }
   /**
    * Quit function: quit the application.
    */
   private void quit()
   {
     System.exit(0);
   }
   /**
    * 'Darker' function: make the picture darker.
    */
   private void makeDarker()
   {
     if(currentImage != null) {
       currentImage.darker();
       frame.repaint();
       showStatus("Applied: darker");
     }
     else {
       showStatus("No image loaded.");
     }
   }
   /**
    * 'Lighter' function: make the picture lighter
    */
   private void makeLighter()
   {
     if(currentImage != null) {
       currentImage.lighter();
       frame.repaint();
       showStatus("Applied: lighter");
     }
     else {
       showStatus("No image loaded.");
     }
   }
   /**
    * 'threshold' function: apply the threshold filter
    */
   private void threshold()
   {
     if(currentImage != null) {
       currentImage.threshold();
       frame.repaint();
       showStatus("Applied: threshold");
     }
     else {
       showStatus("No image loaded.");
     }
   }
   /**
    * 'Lighter' function: make the picture lighter
    */
   private void showAbout()
   {
     JOptionPane.showMessageDialog(frame,
           "ImageViewer\n" + VERSION,
           "About ImageViewer",
           JOptionPane.INFORMATION_MESSAGE);
   }
   // ---- support methods ----
   /**
    * Display a file name on the appropriate label.
    * @param filename The file name to be displayed.
    */
   private void showFilename(String filename)
   {
     if(filename == null) {
       filenameLabel.setText("No file displayed.");
     }
     else {
       filenameLabel.setText("File: " + filename);
     }
   }
   /**
    * Display a status message in the frame's status bar.
    * @param text The status message to be displayed.
    */
   private void showStatus(String text)
   {
     statusLabel.setText(text);
   }
   // ---- swing stuff to build the frame and all its components ----
   /**
    * Create the Swing frame and its content.
    */
   private void makeFrame()
   {
     frame = new JFrame("ImageViewer");
     makeMenuBar(frame);
     Container contentPane = frame.getContentPane();
     // Specify the layout manager with nice spacing
     contentPane.setLayout(new BorderLayout(6, 6));
     filenameLabel = new JLabel();
     contentPane.add(filenameLabel, BorderLayout.NORTH);
     imagePanel = new ImagePanel();
     contentPane.add(imagePanel, BorderLayout.CENTER);
     statusLabel = new JLabel(VERSION);
     contentPane.add(statusLabel, BorderLayout.SOUTH);
     // building is done - arrange the components and show
     showFilename(null);
     frame.pack();
     Dimension d = Toolkit.getDefaultToolkit().getScreenSize();
     frame.setLocation(d.width/2 - frame.getWidth()/2, d.height/2 - frame.getHeight()/2);
     frame.setVisible(true);
   }
   /**
    * Create the main frame's menu bar.
    * @param frame  The frame that the menu bar should be added to.
    */
   private void makeMenuBar(JFrame frame)
   {
     final int SHORTCUT_MASK =
       Toolkit.getDefaultToolkit().getMenuShortcutKeyMask();
     JMenuBar menubar = new JMenuBar();
     frame.setJMenuBar(menubar);
     JMenu menu;
     JMenuItem item;
     // create the File menu
     menu = new JMenu("File");
     menubar.add(menu);
     item = new JMenuItem("Open");
       item.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_O, SHORTCUT_MASK));
       item.addActionListener(new ActionListener() {
                 public void actionPerformed(ActionEvent e) { openFile(); }
               });
     menu.add(item);
     item = new JMenuItem("Close");
       item.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_W, SHORTCUT_MASK));
       item.addActionListener(new ActionListener() {
                 public void actionPerformed(ActionEvent e) { close(); }
               });
     menu.add(item);
     menu.addSeparator();
     item = new JMenuItem("Quit");
       item.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_Q, SHORTCUT_MASK));
       item.addActionListener(new ActionListener() {
                 public void actionPerformed(ActionEvent e) { quit(); }
               });
     menu.add(item);
     // create the Filter menu
     menu = new JMenu("Filter");
     menubar.add(menu);
     item = new JMenuItem("Darker");
       item.addActionListener(new ActionListener() {
                 public void actionPerformed(ActionEvent e) { makeDarker(); }
               });
     menu.add(item);
     item = new JMenuItem("Lighter");
       item.addActionListener(new ActionListener() {
                 public void actionPerformed(ActionEvent e) { makeLighter(); }
               });
     menu.add(item);
     item = new JMenuItem("Threshold");
       item.addActionListener(new ActionListener() {
                 public void actionPerformed(ActionEvent e) { threshold(); }
               });
     menu.add(item);
     // create the Help menu
     menu = new JMenu("Help");
     menubar.add(menu);
     item = new JMenuItem("About ImageViewer...");
       item.addActionListener(new ActionListener() {
                 public void actionPerformed(ActionEvent e) { showAbout(); }
               });
     menu.add(item);
   }
 }