getting around the null problem with a silly canvas for World

svn: r7093

collects/htdch/draw/SillyCanvas.java

@@ -0,0 +1,43 @@
+package draw;
+
+import geometry.*;
+import colors.*;
+
+public class SillyCanvas extends Canvas {
+    private int x = 20; 
+    private int y = 20; 
+
+    private boolean warning() {
+	return super.drawString(new Posn(x,y),"This is a Dummy Canvas.");
+    }
+
+    SillyCanvas(int w, int h) { 
+	super(w,h); 
+	if ((w < x) || (h < y)) 
+	    throw new RuntimeException("SillyCanvas: bad size");
+    }
+
+    public boolean drawCircle(Posn p, int r, AColor c) {
+	return super.drawCircle(p,r,c) && warning(); 
+    }
+
+    public boolean drawDisk(Posn p, int r, AColor c) {
+	return super.drawDisk(p,r,c) && warning(); 
+    }
+
+    public boolean drawRect(Posn p, int width, int height, AColor c) {
+	return super.drawRect(p,width,height,c) && warning(); 
+    }
+
+    public boolean drawLine(Posn p0, Posn p1, AColor c) {
+	return super.drawLine(p0,p1,c) && warning();
+    }
+
+    public boolean drawString(Posn p, String s) { 
+	return super.drawString(p,s) && warning(); 
+    }
+
+    public boolean show() {
+	return super.show() && warning(); 
+    }
+}

collects/htdch/draw/World.java

@@ -1,7 +1,7 @@
 package draw;
 
 public abstract class World {
-    protected Canvas theCanvas = null; // can I do better here? 
+    protected Canvas theCanvas = new SillyCanvas(600,600); // can I do better here? 
     
     /** 
      *@author Matthias Felleisen, Kathy Gray 

collects/htdch/draw/installer.ss

@@ -19,5 +19,6 @@
                                (build-path draw-path file)
                                #f #f)))))
         (javac "Canvas.java")
+        (javac "SillyCanvas.java")
         (javac "World.java")))))