Automatic entry in text field

Question

I have this GUI:

I would like after I enter a number in the Length of hot tub text box for that number to be automatically entered into the Width of hot tub text box, but only if the Round Tub radio button is selected.

public void createHotTubs()   
{   
    hotTubs = new JPanel();   
    hotTubs.setLayout(null);   
    labelTubStatus = new JTextArea(6, 30);   
    hotTubs.add(labelTubStatus);   
    JLabel lengthLabel = new JLabel(   
            "Length of hot tub(ft):");   
    lengthLabel.setBounds(10, 15, 260, 20);   
    hotTubs.add(lengthLabel);   
    hotTubLengthText = new JTextField();   
    hotTubLengthText.setBounds(180, 15, 150, 20);   
    hotTubs.add(hotTubLengthText);   
    JLabel widthLabel = new JLabel(   
            "Width of hot tub(ft):");   
    widthLabel.setBounds(10, 40, 260, 20);   
    hotTubs.add(widthLabel);   
    hotTubWidthText = new JTextField();   
    hotTubWidthText.setBounds(180, 40, 150, 20);   
    hotTubs.add(hotTubWidthText);   
    JLabel depthLabel = new JLabel(   
            "Average depth the hot tub(ft):");   
    depthLabel.setBounds(10, 65, 260, 20);   
    hotTubs.add(depthLabel);   
    hotTubDepthText = new JTextField();   
    hotTubDepthText.setBounds(180, 65, 150, 20);   
    hotTubs.add(hotTubDepthText);   
    JLabel volumeLabel = new JLabel("The hot tub volume is:(ft ^3");   
    volumeLabel.setBounds(10, 110, 260, 20);   
    hotTubs.add(volumeLabel);   
    hotTubVolumeText = new JTextField();   
    hotTubVolumeText.setBounds(180, 110, 150, 20);   
    hotTubVolumeText.setEditable(false);   
    hotTubs.add(hotTubVolumeText);   
    final JRadioButton rdbtnRoundTub = new JRadioButton("Round Tub");   
    rdbtnRoundTub.addActionListener(new ActionListener()   
    {   
        public void actionPerformed(ActionEvent arg0)   
        {   
            hotTubWidthText.setEditable(false);   
        }   
    });   
    rdbtnRoundTub.setSelected(true);   
    rdbtnRoundTub.setBounds(79, 150, 109, 23);   
    hotTubs.add(rdbtnRoundTub);   
    JRadioButton rdbtnOvalTub = new JRadioButton("Oval Tub");   
    rdbtnOvalTub.addActionListener(new ActionListener()   
    {   
        public void actionPerformed(ActionEvent arg0)   
        {   
            hotTubWidthText.setEditable(true);   
        }   
    });   
    rdbtnOvalTub.setBounds(201, 150, 109, 23);   
    hotTubs.add(rdbtnOvalTub);   
    ButtonGroup radioBtnGroup = new ButtonGroup();   
    radioBtnGroup.add(rdbtnRoundTub);   
    radioBtnGroup.add(rdbtnOvalTub);   
    JButton btnCalculateVlmn = new JButton("Calculate Volume");   
    btnCalculateVlmn.addActionListener(new ActionListener()   
    {   
        public void actionPerformed(ActionEvent arg0)   
        {   
            double width = 0, length = 0, depth = 0, volume = 0;    
            String lengthString, widthString, depthString;    
            lengthString = hotTubLengthText.getText();    
            widthString = hotTubWidthText.getText();    
            depthString = hotTubDepthText.getText();    
            depth = Double.valueOf(depthString);  
            length = Double.valueOf(lengthString);  
            width = Double.valueOf(widthString); 

            try  
            {   
                if (rdbtnRoundTub.isSelected())   
                {   
                   volume = length * width * depth;   
                }   
                else  
                {   
                    volume = Math.PI * length * width / 4 * depth;   
                }   
                DecimalFormat formatter = new DecimalFormat("#,###,###.###");   
                hotTubVolumeText.setText("" + formatter.format(volume));   
            }   
            catch (NumberFormatException e)   
            {   
                labelTubStatus   
                        .setText("Enter all three numbers!!");   
            }   
        }   
    });

Answer 1

Add a focus listener to your length text field when it loses focus and the round tub is selected, compute and set the the width.