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Java in a Nutshell

Previous Chapter 8
New AWT Features

8.5 New Feature Demo

Example 8.1 demonstrates all the new AWT features discussed in this chapter. It is quite a long example, but is worth reading over carefully. In addition to demonstrating AWT features, it also shows the use of object serialization to save and load application state, which is discussed in Chapter 9, Object Serialization.

Example 8.1: New AWT Feature Demo for Java 1.1

import java.awt.*;               // ScrollPane, PopupMenu, MenuShortcut, etc.
import java.awt.datatransfer.*;  // Clipboard, Transferable, DataFlavor, etc.
import java.awt.event.*;         // New event model.
import java.io.*;                // Object serialization streams.
import java.util.zip.*;          // Data compression/decompression streams.
import java.util.Vector;         // To store the scribble in.
import java.util.Properties;     // To store printing preferences in.
 * This class places a Scribble component in a ScrollPane container,
 * puts the ScrollPane in a window, and adds a simple pulldown menu system.
 * The menu uses menu shortcuts.  Events are handled with anonymous classes.
public class ScribbleFrame extends Frame {
  /** A very simple main() method for our program. */
  public static void main(String[] args) { new ScribbleFrame(); }
  /** Remember # of open windows so we can quit when last one is closed. */
  protected static int num_windows = 0;
  /** Create a Frame, Menu, and ScrollPane for the scribble component. */
  public ScribbleFrame() {
    super("ScribbleFrame");                  // Create the window.
    num_windows++;                           // Count it.
    ScrollPane pane = new ScrollPane();      // Create a ScrollPane.
    pane.setSize(300, 300);                  // Specify its size.
    this.add(pane, "Center");                // Add it to the frame.
    Scribble scribble;
    scribble = new Scribble(this, 500, 500); // Create a bigger scribble area.
    pane.add(scribble);                      // Add it to the ScrollPane.
    MenuBar menubar = new MenuBar();         // Create a menubar.
    this.setMenuBar(menubar);                // Add it to the frame.
    Menu file = new Menu("File");            // Create a File menu.
    menubar.add(file);                       // Add to menubar.
    // Create three menu items, with menu shortcuts, and add to the menu.
    MenuItem n, c, q;
    file.add(n = new MenuItem("New Window", new MenuShortcut(KeyEvent.VK_N)));
    file.add(c = new MenuItem("Close Window",new MenuShortcut(KeyEvent.VK_W)));
    file.addSeparator();                     // Put a separator in the menu.
    file.add(q = new MenuItem("Quit", new MenuShortcut(KeyEvent.VK_Q)));
    // Create and register action listener objects for the three menu items.
    n.addActionListener(new ActionListener() {     // Open a new window.
      public void actionPerformed(ActionEvent e) { new ScribbleFrame(); }
    c.addActionListener(new ActionListener() {     // Close this window.
      public void actionPerformed(ActionEvent e) { close(); }
    q.addActionListener(new ActionListener() {     // Quit the program.
      public void actionPerformed(ActionEvent e) { System.exit(0); }
    // Another event listener, this one to handle window close requests.
    this.addWindowListener(new WindowAdapter() {
      public void windowClosing(WindowEvent e) { close(); }
    // Set the window size and pop it up.
  /** Close a window.  If this is the last open window, just quit. */
  void close() {
    if (--num_windows == 0) System.exit(0);
    else this.dispose();
 * This class is a custom component that supports scribbling.  It also has
 * a popup menu that allows the scribble color to be set and provides access
 * to printing, cut-and-paste, and file loading and saving facilities.
 * Note that it extends Component rather than Canvas, making it "lightweight."
class Scribble extends Component implements ActionListener {
  protected short last_x, last_y;                // Coordinates of last click.
  protected Vector lines = new Vector(256,256);  // Store the scribbles.
  protected Color current_color = Color.black;   // Current drawing color.
  protected int width, height;                   // The preferred size.
  protected PopupMenu popup;                     // The popup menu.
  protected Frame frame;                         // The frame we are within.
  /** This constructor requires a Frame and a desired size */
  public Scribble(Frame frame, int width, int height) {
    this.frame = frame;
    this.width = width;
    this.height = height;
    // We handle scribbling with low-level events, so we must specify
    // which events we are interested in.
    // Create the popup menu using a loop.  Note the separation of menu
    // "action command" string from menu label.  Good for internationalization.
    String[] labels = new String[] {
      "Clear", "Print", "Save", "Load", "Cut", "Copy", "Paste" };
    String[] commands = new String[] {
      "clear", "print", "save", "load", "cut", "copy", "paste" };
    popup = new PopupMenu();                   // Create the menu.
    for(int i = 0; i < labels.length; i++) {
      MenuItem mi = new MenuItem(labels[i]);   // Create a menu item.
      mi.setActionCommand(commands[i]);        // Set its action command.
      mi.addActionListener(this);              // And its action listener.
      popup.add(mi);                           // Add item to the popup menu.
    Menu colors = new Menu("Color");           // Create a submenu.
    popup.add(colors);                         // And add it to the popup.
    String[] colornames = new String[] { "Black", "Red", "Green", "Blue"};
    for(int i = 0; i < colornames.length; i++) {
      MenuItem mi = new MenuItem(colornames[i]);  // Create the submenu items
      mi.setActionCommand(colornames[i]);         // in the same way.
    // Finally, register the popup menu with the component it appears over.
  /** Specifies how big the component would like to be.  It always returns the
   *  preferred size passed to the Scribble() constructor. */
  public Dimension getPreferredSize() { return new Dimension(width, height); }
  /** This is the ActionListener method invoked by the popup menu items. */
  public void actionPerformed(ActionEvent event) {
    // Get the "action command" of the event, and dispatch based on that.
    // This method calls a lot of the interesting methods in this class.
    String command = event.getActionCommand();
    if (command.equals("clear")) clear();
    else if (command.equals("print")) print();
    else if (command.equals("save")) save();
    else if (command.equals("load")) load();
    else if (command.equals("cut")) cut();
    else if (command.equals("copy")) copy();
    else if (command.equals("paste")) paste();
    else if (command.equals("Black")) current_color = Color.black;
    else if (command.equals("Red")) current_color = Color.red;
    else if (command.equals("Green")) current_color = Color.green;
    else if (command.equals("Blue")) current_color = Color.blue;
  /** Draw all the saved lines of the scribble, in the appropriate colors. */
  public void paint(Graphics g) {
    for(int i = 0; i < lines.size(); i++) {
      Line l = (Line)lines.elementAt(i);
      g.drawLine(l.x1, l.y1, l.x2, l.y2);
   * This is the low-level event-handling method called on mouse events
   * that do not involve mouse motion.  Note the use of isPopupTrigger()
   * to check for the platform-dependent popup menu posting event, and of
   * the show() method to make the popup visible.  If the menu is not posted,
   * then this method saves the coordinates of a mouse click or invokes
   * the superclass method.
  public void processMouseEvent(MouseEvent e) {
    if (e.isPopupTrigger())                               // If popup trigger,
      popup.show(this, e.getX(), e.getY());               // pop up the menu.
    else if (e.getID() == MouseEvent.MOUSE_PRESSED) {
      last_x = (short)e.getX(); last_y = (short)e.getY(); // Save position.
    else super.processMouseEvent(e);  // Pass other event types on.
   * This method is called for mouse motion events.  It adds a line to the
   * scribble, on screen, and in the saved representation.
  public void processMouseMotionEvent(MouseEvent e) {
    if (e.getID() == MouseEvent.MOUSE_DRAGGED) {
      Graphics g = getGraphics();                     // Object to draw with.
      g.setColor(current_color);                      // Set the current color.
      g.drawLine(last_x, last_y, e.getX(), e.getY()); // Draw this line
      lines.addElement(new Line(last_x, last_y,       // and save it, too.
                                (short) e.getX(), (short)e.getY(),
      last_x = (short) e.getX();  // Remember current mouse coordinates.
      last_y = (short) e.getY();
    else super.processMouseMotionEvent(e);  // Important!
  /** Clear the scribble.  Invoked by popup menu. */
  void clear() {
    lines.removeAllElements();   // Throw out the saved scribble
    repaint();                   // and redraw everything.
  /** Print out the scribble.  Invoked by popup menu. */
  void print() {
    // Obtain a PrintJob object.  This posts a Print dialog.
    // printprefs (created below) stores user printing preferences.
    Toolkit toolkit = this.getToolkit();
    PrintJob job = toolkit.getPrintJob(frame, "Scribble", printprefs);
    // If the user clicked Cancel in the print dialog, then do nothing.
    if (job == null) return;
    // Get a Graphics object for the first page of output.
    Graphics page = job.getGraphics();
    // Check the size of the scribble component and of the page.
    Dimension size = this.getSize();
    Dimension pagesize = job.getPageDimension();
    // Center the output on the page.  Otherwise it would be
    // scrunched up in the upper-left corner of the page.
    page.translate((pagesize.width - size.width)/2,
                   (pagesize.height - size.height)/2);
    // Draw a border around the output area, so it looks neat.
    page.drawRect(-1, -1, size.width+1, size.height+1);
    // Set a clipping region so our scribbles don't go outside the border.
    // On-screen this clipping happens automatically, but not on paper.
    page.setClip(0, 0, size.width, size.height);
    // Print this Scribble component.  By default this will just call paint().
    // This method is named print(), too, but that is just coincidence.
    // Finish up printing.
    page.dispose();   // End the page--send it to the printer.
    job.end();        // End the print job.
  /** This Properties object stores the user print dialog settings. */
  private static Properties printprefs = new Properties();
   * The DataFlavor used for our particular type of cut-and-paste data.
   * This one will transfer data in the form of a serialized Vector object.
   * Note that in Java 1.1.1, this works intra-application, but not between
   * applications.  Java 1.1.1 inter-application data transfer is limited to
   * the pre-defined string and text data flavors.
  public static final DataFlavor dataFlavor =
      new DataFlavor(Vector.class, "ScribbleVectorOfLines");
   * Copy the current scribble and store it in a SimpleSelection object
   * (defined below).  Then put that object on the clipboard for pasting.
  public void copy() {
    // Get system clipboard.
    Clipboard c = this.getToolkit().getSystemClipboard();
    // Copy and save the scribble in a Transferable object.
    SimpleSelection s = new SimpleSelection(lines.clone(), dataFlavor);
    // Put that object on the clipboard.
    c.setContents(s, s);
  /** Cut is just like a copy, except we erase the scribble afterwards. */
  public void cut() { copy(); clear();  }
   * Ask for the Transferable contents of the system clipboard, then ask that
   * object for the scribble data it represents.  If either step fails, beep!
  public void paste() {
    Clipboard c = this.getToolkit().getSystemClipboard();  // Get clipboard.
    Transferable t = c.getContents(this);                  // Get its contents.
    if (t == null) {              // If there is nothing to paste, beep.
    try {
      // Ask for clipboard contents to be converted to our data flavor.
      // This will throw an exception if our flavor is not supported.
      Vector newlines = (Vector) t.getTransferData(dataFlavor);
      // Add all those pasted lines to our scribble.
      for(int i = 0; i < newlines.size(); i++)
      // And redraw the whole thing.
    catch (UnsupportedFlavorException e) {
      this.getToolkit().beep();   // If clipboard has some other type of data
    catch (Exception e) {
      this.getToolkit().beep();   // Or if anything else goes wrong...
   * This nested class implements the Transferable and ClipboardOwner
   * interfaces used in data transfer.  It is a simple class that remembers a
   * selected object and makes it available in only one specified flavor.
  static class SimpleSelection implements Transferable, ClipboardOwner {
    protected Object selection;    // The data to be transferred.
    protected DataFlavor flavor;   // The one data flavor supported.
    public SimpleSelection(Object selection, DataFlavor flavor) {
      this.selection = selection;  // Specify data.
      this.flavor = flavor;        // Specify flavor.
    /** Return the list of supported flavors.  Just one in this case. */
    public DataFlavor[] getTransferDataFlavors() {
      return new DataFlavor[] { flavor };
    /** Check whether we support a specified flavor. */
    public boolean isDataFlavorSupported(DataFlavor f) {
      return f.equals(flavor);
    /** If the flavor is right, transfer the data (i.e., return it). */
    public Object getTransferData(DataFlavor f)
         throws UnsupportedFlavorException {
      if (f.equals(flavor)) return selection;
      else throw new UnsupportedFlavorException(f);
    /** This is the ClipboardOwner method.  Called when the data is no
     *  longer on the clipboard.  In this case, we don't need to do much. */
    public void lostOwnership(Clipboard c, Transferable t) {
      selection = null;
   * Prompt the user for a filename, and save the scribble in that file.
   * Serialize the vector of lines with an ObjectOutputStream.
   * Compress the serialized objects with a GZIPOutputStream.
   * Write the compressed, serialized data to a file with a FileOutputStream.
   * Don't forget to flush and close the stream.
  public void save() {
    // Create a file dialog to query the user for a filename.
    FileDialog f = new FileDialog(frame, "Save Scribble", FileDialog.SAVE);
    f.show();                        // Display the dialog and block.
    String filename = f.getFile();   // Get the user's response
    if (filename != null) {          // If user didn't click "Cancel."
      try {
        // Create the necessary output streams to save the scribble.
        FileOutputStream fos = new FileOutputStream(filename); // Save to file.
        GZIPOutputStream gzos = new GZIPOutputStream(fos);     // Compress.
        ObjectOutputStream out = new ObjectOutputStream(gzos); // Save objects.
        out.writeObject(lines);      // Write the entire vector of scribbles.
        out.flush();                 // Always flush the output.
        out.close();                 // And close the stream.
      // Print out exceptions.  We should really display them in a dialog...
      catch (IOException e) { System.out.println(e); }
   * Prompt for a filename, and load a scribble from that file.
   * Read compressed, serialized data with a FileInputStream.
   * Uncompress that data with a GZIPInputStream.
   * Deserialize the vector of lines with an ObjectInputStream.
   * Replace current data with new data, and redraw everything.
  public void load() {
    // Create a file dialog to query the user for a filename.
    FileDialog f = new FileDialog(frame, "Load Scribble", FileDialog.LOAD);
    f.show();                         // Display the dialog and block.
    String filename = f.getFile();    // Get the user's response
    if (filename != null) {           // If user didn't click "Cancel."
      try {
        // Create necessary input streams.
        FileInputStream fis = new FileInputStream(filename); // Read from file.
        GZIPInputStream gzis = new GZIPInputStream(fis);     // Uncompress.
        ObjectInputStream in = new ObjectInputStream(gzis);  // Read objects
        // Read in an object.  It should be a vector of scribbles.
        Vector newlines = (Vector)in.readObject();
        in.close();                    // Close the stream.
        lines = newlines;              // Set the Vector of lines.
        repaint();                     // And redisplay the scribble.
      // Print out exceptions.  We should really display them in a dialog...
      catch (Exception e) { System.out.println(e); }
  /** A class to store the coordinates and color of one scribbled line.
   *  The complete scribble is stored as a vector of these objects. */
  static class Line implements Serializable {
    public short x1, y1, x2, y2;
    public Color color;
    public Line(short x1, short y1, short x2, short y2, Color c) {
      this.x1 = x1; this.y1 = y1; this.x2 = x2; this.y2 = y2; this.color = c;

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