Subclassing Graphics2D

[Garrett Rowe]

One article that I read about testing GUI intensive applications suggested subclassing the Graphics object to provide a textual representation of the calls made on it (http://c2.com/cgi/wiki?ExtremeProgrammingTestingGuiIntensiveApps) my question is, since the Graphics object is propagated by the Swing components that control the rendering of individual controls, how can one substitute a subclass in a coherent manner. One solution I can think of is something like this:

public class FooComponent {

   private final SpecialGraphics2D wrapper;

   public FooComponent(SpecialGraphics2D special) {
       wrapper = special;
   }

   public JComponent getComponent() {
      return new JComponent() {
         @Override
         public void paintComponent(Graphics g) {
            Graphics2D g2d = wrapper.wrap((Graphics2D)g);
            doStuffWith(g2d)
         }
      };
   }
   
   //Elsewhere
   String log = wrapper.logString();
}

But since you would have to add the boilerplate to every GUI class, that seems a bit clumsy. Is there a better way where the Graphics subclass will automatically get propogated throughout the system?

[Ulf Dittmer]

I don't have an answer to that, but here's a library that contains several subclasses of Graphics2D; maybe its source code provides some clues.

[Garrett Rowe]

Thanks for the link Ulf. Looking at the tutorials for that library, the two use cases that I see are either constructing the Graphics2D subclass and calling paint(Graphics) directly with the newly created subclass.

SpecialGraphics graph = new SpecialGraphics();
myPanel.paint(graph)

Or wrapping the Graphics object inside an overridden paint(Graphics) method:

@Override
public void paint(Graphics g) {
   SpecialGraphics graph = new SpecialGraphics(g);
   //do stuff here...
}

I guess the first version would be better for the unit testing strategy discussed in the link. That was so simple I don't know why it was escaping me.