Anyone have/know of a method that would format a textbox?

Question

Hi all,
I'm currently trying to make a java tax program. It's not finished, obviously. I'm using ready to program. Here is what I want to do. I want to take the amount in the subtotal box, and as the user is typing, after the key is pressed, the program will check to see if it is an actual number, and if there are strings in it, the computer will automatically knock them out and leave a number. Now, this is supposed to be a currency amount... Any suggestions? Here is my code:
// The "JavaTax" class.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.text.*;
import java.text.DecimalFormat;
public class JavaTax extends JFrame
    private Container contents;
    private JLabel amount, total, gsttotal, psttotal, hsttotal, qsttotal;
    private JTextField amountBox, totalBox, gsttotalBox, psttotalBox, hsttotalBox, qsttotalBox;
    private JPanel totals, selection;
    private JButton calc;
    private JCheckBox gst, hst, pst, qst;
    private JComboBox pstProvinces, hstProvinces;
    private String provincesPST[] = new String [5];
    private String provincesHST[] = new String [3];
    private double QSTRATE = 7.5;
    double subTotal = 0;
    public JavaTax ()
        super ("Java Tax");
        contents = getContentPane ();
        contents.setLayout (new BorderLayout ());
        provincesPST [0] = "British Columbia (7%)";
        provincesPST [1] = "Saskatchewan (5%)";
        provincesPST [2] = "Manitoba (7%)";
        provincesPST [3] = "Ontario (8%)";
        provincesPST [4] = "Prince Edward Island (10%)";
        provincesHST [0] = "New Brunswick (13%)";
        provincesHST [1] = "Newfoundland (13%)";
        provincesHST [2] = "Nova Scotia (13%)";
        hsttotal = new JLabel ("HST Total:", JLabel.RIGHT);
        qsttotal = new JLabel ("QST Total:", JLabel.RIGHT);
        gsttotal = new JLabel ("GST Total:", JLabel.RIGHT);
        psttotal = new JLabel ("PST Total:", JLabel.RIGHT);
        total = new JLabel ("Total:", JLabel.RIGHT);
        amount = new JLabel ("Amount:", JLabel.RIGHT);
        psttotalBox = new JTextField ("", 10);
        psttotalBox.setEditable (false);
        hsttotalBox = new JTextField ("", 10);
        hsttotalBox.setEditable (false);
        gsttotalBox = new JTextField ("", 10);
        gsttotalBox.setEditable (false);
        qsttotalBox = new JTextField ("", 10);
        qsttotalBox.setEditable (false);
        totalBox = new JTextField ("", 10);
        amountBox = new JTextField ("", 10);
        calc = new JButton ("Calculate");
        gst = new JCheckBox ("GST");
        pst = new JCheckBox ("PST");
        hst = new JCheckBox ("HST");
        qst = new JCheckBox ("QST");
        pstProvinces = new JComboBox (provincesPST);
        hstProvinces = new JComboBox (provincesHST);
        //HST only in NB, Newfoundland and NS (all 13%)
        //QST only in Quebec (7.5%)
        // sample = new JLabel (new ImageIcon("file.jpg"))
        hsttotal.setForeground (Color.BLACK);
        psttotal.setForeground (Color.BLACK);
        gsttotal.setForeground (Color.BLACK);
        total.setForeground (Color.BLACK);
        amount.setForeground (Color.BLACK);
        hsttotal.setOpaque (true);
        gsttotal.setOpaque (true);
        psttotal.setOpaque (true);
        total.setOpaque (true);
        amount.setOpaque (true);
        totals = new JPanel ();
        totals.setLayout (new GridLayout (6, 2, 2, 10));
        contents.add (totals, BorderLayout.WEST);
        totals.add (amount);
        totals.add (amountBox);
        totals.add (gsttotal);
        totals.add (gsttotalBox);
        totals.add (psttotal);
        totals.add (psttotalBox);
        totals.add (hsttotal);
        totals.add (hsttotalBox);
        totals.add (qsttotal);
        totals.add (qsttotalBox);
        totals.add (total);
        totals.add (totalBox);
        selection = new JPanel (new GridLayout (7, 1, 2, 10));
        contents.add (selection, BorderLayout.EAST);
        selection.add (gst);
        selection.add (pst);
        selection.add (pstProvinces);
        selection.add (hst);
        selection.add (hstProvinces);
        selection.add (qst);
        selection.add (calc);
        setSize (500, 350);
        setVisible (true);
        NormalTaxHandler nth = new NormalTaxHandler ();
        SpecialTaxHandler sth = new SpecialTaxHandler ();
        TextFieldHandler tfh = new TextFieldHandler ();
        gst.addItemListener (nth);
        pst.addItemListener (nth);
        hst.addItemListener (sth);
        qst.addItemListener (sth);
        amountBox.addKeyListener (tfh);
    public static void main (String[] args)
        JavaTax guey = new JavaTax ();
        guey.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
    } // main method
    public class TextFieldHandler implements KeyListener
        //implementation of KeyListener methods
        public void keyPressed (KeyEvent e)
        public void keyReleased (KeyEvent e)
            check (e);
        public void keyTyped (KeyEvent e)
        public void check (KeyEvent e)
            try
                subTotal = Double.parseDouble (amountBox.getText ());
                DecimalFormat df = new DecimalFormat ("#.##");
                //subTotal =
                //subTotal = subTotal * 100;
                //subTotal = ((int)subTotal)/100;
                amountBox.setText (String.valueOf (df.format (subTotal)));
                subTotal = Double.parseDouble (amountBox.getText ());
            catch (NumberFormatException nfe)
                DecimalFormat df = new DecimalFormat ("#.##");
                amountBox.setText (String.valueOf (df.format (subTotal)));
                subTotal = Double.parseDouble (amountBox.getText ());
            subTotal = Double.parseDouble (amount);
            subTotal = subTotal * 100;
            subTotal = (int) subTotal / 100;
    private class NormalTaxHandler implements ItemListener
        public void itemStateChanged (ItemEvent ie)
            JCheckBox source = (JCheckBox) ie.getSource ();
            // If the object is selected . . .
            if (ie.getStateChange () == ItemEvent.SELECTED)
                qst.setVisible (false);
                hst.setVisible (false);
                hstProvinces.setVisible (false);
            else
                if (pst.isSelected () == false && gst.isSelected () == false)
                    qst.setVisible (true);
                    hst.setVisible (true);
                    hstProvinces.setVisible (true);
    private class SpecialTaxHandler implements ItemListener
        public void itemStateChanged (ItemEvent ie)
            JCheckBox source = (JCheckBox) ie.getSource ();
            if (ie.getStateChange () == ItemEvent.SELECTED)
                gst.setVisible (false);
                pst.setVisible (false);
                pstProvinces.setVisible (false);
                if (qst.isSelected () == true && hst.isSelected () == false)
                    hst.setVisible (false);
                    hstProvinces.setVisible (false);
                else if (hst.isSelected () == true && qst.isSelected () == false)
                    qst.setVisible (false);
            else
                if (hst.isSelected () == false || qst.isSelected () == false)
                    gst.setVisible (true);
                    pst.setVisible (true);
                    pstProvinces.setVisible (true);
                    hst.setVisible (true);
                    qst.setVisible (true);
                    hstProvinces.setVisible (true);
     * Create a MaskFormatter for FormattedTextFields
    protected MaskFormatter createFormatter (String s)
        MaskFormatter formatter = null;
        try
            formatter = new MaskFormatter (s);
        } // try
        catch (java.text.ParseException exc)
        } // catch
        return formatter;
    } // MaskFormatter method
} // GUI class

Answer 1

You can use Integer.parseInt(String) (or Double.parseDouble(String), etc.) to check if the String represents a number.
http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Integer.html#parseInt(java.lang.String)
If it doesn't, you can use Character.isDigit(char) to check each char, and substring them out if they aren't digits. Then parse it again.
http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Character.html#isDigit(char)