In the Javadocs for Graphics2D, it says that it's the "fundamental class
for rendering 2-dimensional shapes, text and images" and therefore leads
me to believe it's reliable.  That article, however, seems to suggest
overriding the paint method, which is generally not advisable in Swing.  
You should normally override the paintComponent method instead.

= Steve =

The class hierarchy seems to be as follows:

java.awt.Graphics (abstract)

`- javax.swing.SystemEventQueueUtilities.RunnableCanvasGraphics (static
private inner)

   DebugGraphics seem to only come up if you turn on debuging for your
component via the setDebugGraphicsOptions() method.

   I couldn't find sun.print.ProxyGraphics being used anywhere, and given
the package name, it's probably for "internal use only".

   RunnableCanvasGraphics has something to do with an optimization for
applets for situations where it is known before hand that no painting will
be done, so you should never actually see an instance of this.

   So basically, the only situation you have to worry about is
DebugGraphics. As long as you never touch the setDebugGraphicsOptions()
method (and I've never seen a Java program actually use that method), you
should be okay.

   - Oliver

The Graphics object in a JPanel is always a Graphics2D.  I think but
can't find it in the docs that all Swing components are the same.

Deep down somewhere in some Java documentation (AFAIR it was some
JDK/JRE release notes), Sun "guaranteed" that with the introduction of
Java 2D one gets a Graphics2D instead of a Graphics object.

Of course, they screwed it up :-(. At the same time they added
paintComponent(Graphics). It would have been easy to make that a
paintComponent(Graphics2D) in Swing, and also add a
paintComponent(Graphics2D) to AWT.

/Thomas