Building graphical user interfaces - Objects First with Java: A Practical Introduction Using BlueJ - page 384

The most important methods from OFImage for us are:

■ getPixel and setPixel to read and modify single pixels
■ getHeight and getWidth to find out about the image's size.
The ImageFileManager class offers three methods: one to read a named image file from
disk and return it as an OFImage , one to write an OFImage file to disk, and one to open a file-
chooser dialog to let a user select an image to open. The methods can read files in the standard
JPEG and PNG formats, and the save method will write files in JPEG format. This is done us-
ing the standard Java image I/O methods from the ImageIO class (package javax.imageio ).

The ImagePanel class implements a custom-made Swing component to display our image.
Custom-made Swing components can easily be created by writing a subclass of an existing
component. As such, they can be inserted into a Swing container and displayed in our GUI like
any other Swing component. ImagePanel is a subclass of JComponent . The other important
point to note here is that ImagePanel has a setImage method that takes an OFImage as a pa-
rameter to display any given OFImage .

11.5.2 Adding the image

Now that we have prepared the classes for dealing with images, adding the image to the user
interface is easy. Code 11.4 shows the important differences from previous versions.

Code 11.4
ImageViewer class
with ImagePanel

public class ImageViewer
{

private JFrame frame;
private ImagePanel imagePanel;

// Constructor and quit method omitted.

/**
* Open function: open a file chooser to select a new
* image file.
*/
private void openFile()
{

OFImage image = ImageFileManager.getImage();
imagePanel.setImage(image);
frame.pack();

}

/**
* Create the Swing frame and its content.
*/