Java画余弦曲线，哪里异常了

import java.awt.*;import java.awt.event.*;import javax.swing.*;public class yuxian extends JFrame implements ComponentListener,ItemListener{    p rivate JComboBox combobox_color;    public yuxian()    {        super("");        this.setSize(500,500);        this.setDefaultCloseOperation(EXIT_ON_CLOSE);        this.setLayout(new FlowLayout());                Object data[]={Color.red,Color.green,Color.blue};        combobox_color=new JComboBox(data);        combobox_color.addItemListener(this);        this.add(combobox_color);                this.addComponentListener(this);        this.setVisible(true);    }    public void paint(Graphics g)    {        g.setColor((Color)combobox_color.getSelectedItem());        double f(double x)         {            return (Math.cos(x/12.0)*200.0/4+100);          }          for(int x=0;x<this.getWidth();x++)        {            g.drawLine(x,(int)f(x),x+1,(int)f(x+1));        }    }    public void itemStateChanged(ItemEvent e)    {        repaint();    }    public void componentResized(ComponentEvent e)    {        repaint();    }    public void componentMoved(ComponentEvent e){}    public void componentHidden(ComponentEvent e){}    public void componentShown(ComponentEvent e){}    public static void main(String arg[])    {        new yuxian();    }}