Help with JFrame exception

[javaman1]

I am doing an assignment for my AP Java class. We are required to create this GUI program that will ask the user for an input then will add 5% tax, and then output the new total. I have that part working, but I am trying to add an exception handler in the TaxListener that is thrown if the user enters something other than a number. I have got it to compile and run, however it is thrown into an infinite loop in which it creates an infinite number of JFrames. Can someone help me prevent this? I want it to output a single error message JFrame, then the user can close it, and go back to the GUI to input a new number. Thanks!

//************
//Adam Brewer*
//Lab 11     *
//************

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.text.DecimalFormat;

class TaxGUI extends JFrame
{


    private JLabel billLabel = new JLabel("Bill");
    private JLabel totalLabel = new JLabel("Bill + tax");
    private JTextField billField = new JTextField("$00.0");
    private JTextField totalField = new JTextField("$00.0");
    private JButton taxButton = new JButton(">>>>>");

    public TaxGUI()
    {
        JPanel dataPanel = new JPanel(new GridLayout(2,2,20,10));

        dataPanel.add(billLabel);
        dataPanel.add(billField);
        dataPanel.add(totalLabel);
        dataPanel.add(totalField);

        JPanel buttonPanel = new JPanel();
        buttonPanel.add(taxButton);

        Container container = getContentPane();
        container.add(dataPanel, BorderLayout.NORTH);
        container.add(buttonPanel, BorderLayout.SOUTH);

        taxButton.addActionListener(new TaxListener());
    }

    private class TaxListener implements ActionListener
    {
        public void actionPerformed(ActionEvent e)
        {
            double bill = 0;
            while(true)
            {
				try
				{
					String input = billField.getText();
					bill = Double.parseDouble(input);
					break;
				}
				catch(Exception ex)
				{
					JFrame j1 = new JFrame();
					JPanel error = new JPanel();
					JLabel msg = new JLabel("ERROR!");
					error.add(msg);
					j1.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
					j1.setSize(200, 200);
					j1.setTitle("ERROR!");
					Container pane = getContentPane();
					pane.add(error);
					j1.setVisible(true);
				}
			}

            bill = bill + (bill * .05);
            bill = roundTwoDecimals(bill);
            totalField.setText("$" + bill);
        }
    }

    private double roundTwoDecimals(double d)
    {
        DecimalFormat twoDForm = new DecimalFormat("#.##");
        return Double.valueOf(twoDForm.format(d));
    }
}

[StormyWaters]

Change the infinite loop into something that makes sense. I suggest changing the declaration of the variable "bill" to this:

doube bill = -1d;

Then try implementing a do-while loop where you try to obtain the value for bill while the variable bill is not -1d.

[venerik]

Why do you have a while(true) loop in your code? I think you should get rid of that.

Second, there are standard dialogues present in Swing you can use for your error message. No need to construct one yourself.

Erik

[javaman1]

StormyWaters, I don't know anything about do-while loops. :(

venerik, I have been searching the API's and cannot find that method. I assumed there was one. What exactly is it?

[venerik]

JOptionPane.showMessageDialog is the one I meant.