GRAPHICS - Introduction to Java Programming - page 504

94 int xHour = ( int )(xCenter + hLength *
95 Math.sin((hour % 12 + minute / 60.0 ) * ( 2 * Math.PI / 12 )));
96 int yHour = ( int )(yCenter - hLength *
97 Math.cos((hour % 12 + minute / 60.0 ) * ( 2 * Math.PI / 12 )));
98 g.setColor(Color.green);
99 g.drawLine(xCenter, yCenter, xHour, yHour);
100 }
101
102 public void setCurrentTime() {
103 // Construct a calendar for the current date and time
104 Calendar calendar = new GregorianCalendar();
105
106

get current time

// Set current hour, minute, and second

107 this .hour = calendar.get(Calendar.HOUR_OF_DAY);

108 this .minute = calendar.get(Calendar.MINUTE);

109 this .second = calendar.get(Calendar.SECOND);

110 }
111
112 @Override
113

override
getPreferredSize

public Dimension getPreferredSize() {

114 return new Dimension( 200 , 200 );

115 }
116 }

The program enables the clock size to adjust as the frame resizes. Every time you resize the
frame, the paintComponent method is automatically invoked to paint a new clock. The
paintComponent method displays the clock in proportion to the panel width ( getWidth() )
and height ( getHeight() ) (lines 60-63 in StillClock ).

13.10 Displaying Images
You can draw images in a graphics context.

Key
Point

You learned how to create image icons and display them in labels and buttons in Section 12.10,
Image Icons. For example, the following statements create an image icon and display it in a label:

ImageIcon imageIcon = new ImageIcon( "image/us.gif" );
JLabel jlblImage = new JLabel(imageIcon);

An image icon displays a fixed-size image. To display an image in a flexible size, you need to
use the java.awt.Image class. An image can be created from an image icon using the
getImage() method as follows:

Image image = imageIcon.getImage();

Using a label as an area for displaying images is simple and convenient, but you don't have
much control over how the image is displayed. A more flexible way to display images is to
use the drawImage method of the Graphics class on a panel. Four versions of the
drawImage method are shown in Figure 13.22.
ImageObserver specifies a GUI component for receiving notifications of image informa-
tion as the image is constructed. To draw images using the drawImage method in a Swing
component, such as JPanel , override the paintComponent method to tell the component
how to display the image in the panel.
Listing 13.11 gives the code that displays an image from image/us.gif . The file
image/us.gif (line 20) is under the class directory. An Image object is obtained in line 21.
The drawImage method displays the image to fill in the whole panel, as shown in
Figure 13.23.