//更改设置后记得repait(),类似刷新
public void actionPerformed(ActionEvent e) {
if (e.getSource() == butt1) {
can.huanc(Color.red);
can.repaint();//加上这个
} else if (e.getSource() == butt2) {
can.huanc(Color.green);
can.repaint();//加上这个
} else if (e.getSource() == butt3) {
can.huanc(Color.blue);
can.repaint();//加上这个
}
}