Java Foundation Classes in a Nutshell

All of the drawImage() methods of the Graphics objects requir eanjava.awt.-

image.ImageObserver object. This is the object that handles things if you try to

draw an image that is not fully loaded. Fortunately,

java.awt.Component imple-

ments

ImageObserver,soyou can use any Component or Applet object for this

method argument.

If are writing an applet and want to load a predefined image from a URL, you can

use the

getImage() method defined by the java.applet.Applet class. This

method begins downloading the specified image and retur ns an

Image object to

you immediately.

If you are writing a standalone application and want to load a predefined image

fr om a file or URL, use one of the

getImage() or createImage() methods of the

java.awt.Toolkit class:

Toolkit.getDefaultToolkit().getImage("myimage.gif");

Like the getImage() method of Applet, these Toolkit methods start loading the

image and immediately retur nan

Image object. The image formats supported by

these

Applet and Toolkit methods are implementation dependent. Most imple-

mentations support common formats, such as GIF (including transparent GIF),

JPEG, and XBM.

To ensur e that an

Image object is fully loaded before you use it, you can create a

java.awt.MediaTracker object, pass your Image to its addImage() method, then

call the

waitForAll() method.

To create an empty off-scr een image that you can draw into and copy pixels out

of, call the

createImage() method ...