关于画图的几个问题

 menuitem.addactionlistener（new java.awt.event.actionlistener（) {
            public void actionperformed（java.awt.event.actionevent evt) {
                panel.getgraphics.drawline（10,10,100,100);
            }
        });

public void paintcomponent（graphics g) {
        super.paintcomponent（g);
        if （paintwhat == 0) {
            g.drawstring（"now paintwhat is 0", message_x, message_y);
        }
        else if （paintwhat == 1) {
            g.drawstring（"now paintwhat is 1", message_x, message_y);
        }
    }

public void actionperformed（actionevent e) {
        panel.setpaintwhat（1);
        panel.update（panel.getgraphics（));
    }