storing image information using class Image

Class Image is an abstract class—as a result, programs cannot instantiate class Image to create objects. To achieve platform independence, the Java implementation on each plat开发者_运维百科form provides its own subclass of Image to store image information.

The text is about class java.awt.Image.

I don't understand the second part, namely:-

... provides its own subclass of Image to store image information.

Technically, how does that happen?

Image instances are typically created through methods such as Toolkit.createImage(). In this case, the actual instantiation of the Image object is delegated to the Toolkit class, which is platform-dependent.

Note that while you cannot directly instantiate class Image, you can instantiate BufferedImage, which is a concrete Image subclass.

The concrete subclass of Image might, in some cases, be a class which isn't part of the public API of the JDK. (In other cases, you might find that you're getting a BufferedImage, which is much nicer in the event that you intend to do something with the image you get.)

Try System.out.println(img.getClass().getName()); just to see what you're getting.