Learning Java
Chapter 14: Using Swing Components
Here's an example that uses a JScrollPane to display a large
image. The application itself is very simple; all we do is place the image
in an ImageComponent, wrap a JScrollPane around
it, and put the JScrollPane in a JFrame's content
pane. Here's the code:
//file: ScrollPaneFrame.java
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class ScrollPaneFrame {
public static void main(String[] args) {
String filename = "Piazza di Spagna.jpg";
if (args.length > 0)
filename = args[0];
JFrame f = new JFrame("ScrollPaneFrame v1.0");
f.setSize(300, 300);
f.setLocation(200, 200);
f.addWindowListener(new WindowAdapter( ) {
public void windowClosing(WindowEvent e) { System.exit(0); }
});
Image image = Toolkit.getDefaultToolkit( ).getImage(filename);
f.getContentPane( ).add(
new JScrollPane(new ImageComponent(image)));
f.setVisible(true);
}
}
And here's the ImageComponent. It waits for the image to load,
using a MediaTracker, and sets its size to the size of the
image. It also provides a paint( ) method to draw the image.
This takes a single call to drawImage( ). The first argument
is the image itself; the next two are the coordinates of the image relative
to the ImageComponent; and the last is a reference to the
ImageComponent itself (this), which serves as an
image observer. (We'll discuss image observers in Chapter 18, Working
with Images and Other Media; for the time being, take this on
faith.)
//file: ImageComponent.java
import java.awt.*;
import javax.swing.*;
public class ImageComponent extends JComponent {
Image image;
Dimension size;
public ImageComponent(Image image) {
this.image = image;
MediaTracker mt = new MediaTracker(this);
mt.addImage(image, 0);
try {
mt.waitForAll( );
}
catch (InterruptedException e) {
// error ...
};
size = new Dimension (image.getWidth(null),
image.getHeight(null));
setSize(size);
}
public void paint(Graphics g) {
g.drawImage(image, 0, 0, this);
}
public Dimension getPreferredSize( ) {
return size;
}
}
Finally, ImageComponent provides a getPreferredSize(
) method, overriding the method it inherits from
Component. This method simply returns the image's size, which
is a Dimension object. When you're using
JScrollPane, it's important for the object you're scrolling to
provide a reliable indication of its size. Figure 14-6 shows the
ScrollPaneFrame with the ImageComponent.
Figure 14-6. The ScrollPaneFrame application
|
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