Confusion about abstract drawImage-methods in jdk1.3

Question

I have discovered that...
According to jdk1.3 and jdk1.3.1 API there are only abstract drawImage-methods in Graphics and Graphics2D class. That should mean they are not implemented hence you can't use them. Nevertheless they use them on tutorials and i was wondering which of them are actually working?
According to my JBuilder4 there are 2 implemented drawImage-methods in Graphics2D
drawImage(BufferedImage img, BufferedImageOp op, int x, int y) and
drawImage(Image img, AffineTransform xform, ImageObserver obs)
But!
According to tutorials they use
g2.drawImage(bi, 0, 0, this); which means they use
drawImage(BufferedImage img, int x, int y, ImageObserver observer) from the Graphics class
Has anyone tried drawingImages on a Canvas that can explain to me which one to use?

Answer 1

Your confusion is understandable. Let's recap:
* Graphics is an abstract class. This implies that in order for there to be an instance of one, there must be a subclass with a concrete implementation (i.e. all abstract method implemented)
* Graphics2D is an extension of Graphics and is also an abstract class. It adds all the support for the Java2D features, including support for BufferedImage.
So - when you get a graphics context - where is the implementation of the class coming from? The answer is that the Graphics instance you will use is provided by the platform-specific toolkit that your JDK implementation provides.
Incidentally, from JDK 1.2 onward, graphics contexts are guaranteed to be implementations of Graphics2D. This implies that the following conversion will always work:
   public void paintComponent(Graphics g)
       // Guaranteed to work
       Graphics2D g2 = (Graphics2D) g;
       g2.setPaint(Color.orange);
   }As to which version of drawImage() you should use: if your image is not already in a BufferedImage you should use the one that takes an Image as the first parameter.
Mitch Goldstein
Author, Hardcore JFC (Cambridge Univ Press)
[email protected]