How To Update / Refresh JPanel On JButton Click

I am trying to plot a graph and graph should display when JButton is clicked. To create data set, I am taking some value through JTextField and then created a chart and plotted it. I've got a problems: the chart doesn't refresh when I change the text field value.URL....Here is my program:

public class Test2 extends JFrame {
/**
*
*/
private static final long serialVersionUID = 1L;
private JPanel contentPane;
private ChartPanel chartPanel;
private JTextField textField_1;
double a;

[code]....