Creating and Enriching Graphical User Interfaces - Beginning Java 7 - page 618

methodtoloadanddisplaytheimage. ScrollPane 's void doLayout() method
lays out this container by resizing its child (the image canvas) to its preferred size.
Exit'sactionlistenerisinvokedwhentheuserselectsExit.Itinvokes dispose() on
the frame window to dispose of this window's (and the contained components') native
screenresources.Furthermore,awindowclosingeventistriggeredandtheframewin-
dow's window listener's windowClosing() method is invoked.
The main() method creates the GUI on the EDT. It instantiates a scrollpane, and
setsitspreferredsizetoanarbitraryvaluethatservesastheframewindow'sdefaultsize
(following a pack() method call).
The createGUI() method call installs the menubar on its Frame argument, and
returnstheimagecanvas,whichissavedinthe ImageCanvas classfieldsothatitcan
be accessed from the Open menuitem listener. The image canvas is also added to the
scrollpane, and the scrollpane is added to the frame window.
Listing 7-5 presents ImageCanvas .
Listing 7-5 . Displaying a user-selected image
import java.awt.Canvas;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.MediaTracker;
class ImageCanvas extends Canvas
{
private Image image;
@Override
public void paint(Graphics g)
{
// drawImage() does nothing when image contains the
null reference.
g.drawImage(image, 0, 0, null);
}
void setImage(Image image)
{
MediaTracker mt = new MediaTracker(this);
mt.addImage(image, 1);