protected Canvas createCanvas(Composite parent, int style,
PaintListener pl) {
Canvas c = new Canvas(parent, style);
if (pl != null) {
c.addPaintListener(pl);
}
return c;
}
protected Canvas createCanvas(Composite parent, PaintListener pl) {
return createCanvas(parent, SWT.NONE, pl);
}


参考一下这个文章，是说swt的：

http://www-128.ibm.com/developerworks/cn/opensource/os-jface3/