A Canvas paint method is called when isShowing() returns false.

To reproduce :

% cd /usr/local/java/jdk1.2/solaris/demo/jfc/Java2D
% java Java2Demo
click on the Arcs demo to zoom in on the demo. Here's where many Canvases not showing are calling paint. You won't know this until you put in a debug string in J2DCanvas.java paint method. The debug string could look like :

System.out.println(className + isShowing() + getSize());


Here's the source that gets executed on the mouseClick :

TheLayout.java

   101 tabbedPane = new JTabbedPane();
   102 tabbedPane.setFont(new Font("Times New Roman", Font.PLAIN, 1
0));
   103 int index = Java2Demo.tabbedPane.getSelectedIndex();
   104 String s = Java2Demo.tabbedPane.getTitleAt(index);
   105
   106 JPanel tmpP = (JPanel) getComponent(0);
   107 tabbedPane.addTab(s, tmpP);
   108
   109 clonePanels = new JPanel[tmpP.getComponentCount()];
   110 for (int i = 0; i < clonePanels.length; i++) {
   111 clonePanels[i] = new JPanel(new BorderLayout());
   112 className = ((CanvasPanel) tmpP.getComponent(i)).classNa
me;
   113 CanvasPanel cp = new CanvasPanel(this, clonePanels[i]);
   114 if (cp.toolbar != null)
   115 cp.toolbar.addMoreTools();
   116 clonePanels[i].add(cp);
   117 String s1 = className.substring(className.indexOf('.')+1
);
   118 tabbedPane.addTab(s1, clonePanels[i]);
   119 }
   120 p.add(tabbedPane);
   121 remove(tmpP);
   122 add(p);


Here's the Canvas that is drawn :

J2DCanvas.java

   175 public void paint(Graphics g) {
   181 if (!isShowing() || w <= 0 || h <= 0) {
   182 return;
   183 }