Java Reference
In-Depth Information
index.html ) andbrowsingtheJDKdocumentationforthe Component and Con-
tainer classes.
AWT supports GIF, JPEG, and PNG images via java.awt.Image , Toolkit , and
other classes. Because Java 2D largely obviates the need to work with these classes,
I won't discuss AWT's support for images in great detail. However, you should know
something about this support because various JFC classes (such as
javax.swing.ImageIcon )workwith Image ,andevenprovideconstructorsand/
or methods that take Image arguments and (in regard to methods) return Image in-
The Toolkit class declares several createImage() methods for creating and
returning Image objects from various sources. For example, Image cre-
ateImage(String filename) returnsan Image objectthatrepresentstheimage
defined in the file identified by filename .
Toolkit also declares two getImage() methods that create and return Image
objects. Unlike their createImage() counterparts, the getImage() methods
cache Image objects and can return the same object to different callers. This sharing
mechanism helps AWT save heap space, especially when large images are loaded. In
contrast,the createImage() methodsalwaysreturnnew Image objectsthatarenot
shared among callers.
Image objects represent images but do not contain them: a loaded image is asso-
ciated with an Image object. This dichotomy exists because Java was originally used
mainly in a web browser context.
At that time, computers and network connections were much slower than they are
today, and loading large images over the wire was a time-consuming process. Rather
thanforcean applet (abrowser-basedapplication)towaituntilanimagehadcompletely
When you invoke a createImage() or getImage() method, a background
thread is started to load the image, and createImage() / getImage() returns im-
mediately with an Image object.
you cannot immediately obtain the image's width and height, or even draw the entire
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