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?

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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.

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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.