Building graphical user interfaces - Objects First with Java: A Practical Introduction Using BlueJ - page 385

Code 11.4
continued
ImageViewer class
with ImagePanel

private void makeFrame()
{

frame = new JFrame( "ImageViewer" );
makeMenuBar(frame);

Container contentPane = frame.getContentPane();

imagePanel = new ImagePanel();
contentPane.add(imagePanel);

// building is done - arrange the components and show
frame.pack();
frame.setVisible( true );

}

// MakeMenuBar method omitted.
}

When comparing this code with the previous version, we note that there are only two small changes:

■ In method makeFrame , we now create and add an ImagePanel component instead of a
JLabel . Doing this is not more complicated than adding the label. The ImagePanel object
is stored in an instance field so that we can access it again later.
■ Our openFile method has now been changed to actually open and display an image file.
Using our image-processing classes, this also is easy now. The ImageFileManager class
has a method to select and open an image, and the ImagePanel object has a method to dis-
play that image. One thing to note is that we need to call frame.pack() at the end of the
openFile method, as the size of our image component has changed. The pack method will
recalculate the frame layout and redraw the frame so that the size change is properly handled.

Exercise 11.14 Open and test the imageviewer0-4 project. The folder for this chapter's
projects also includes a folder called images . Here, you can find some test images you can
use. Of course, you can also use your own images.

Exercise 11.15 What happens when you open an image and then resize the frame? What if
you first resize the frame and then open an image?

With this version, we have solved the central task; we can now open an image file from disk
and display it on screen. Before we call our project “version 1.0,” however, and thus declare it
finished for the first time, we want to add a few more improvements (see Figure 11.2).

■ We want to add two labels: one to display the image filename at the top and a status text at
the bottom.

■ We want to add a Filter menu that contains some filters that change the image's appearance.
■ We want to add a Help menu that contains an About ImageViewer item. Selecting this menu item
should display a dialog with the application's name, version number, and author information.