Problem detecting JRadioButton action in Mortgage calculator

Posted on 2006-06-10
Last Modified: 2010-03-31
I am having difficulty getting the changes to radio buttons being detected. I have the user interface looking correct and tried using isSelected to tell which radio button is chosen. When a change is detected, I want the program to assign the values in the term and yearlyRate variabes according to that radio button selection. I tried using the same if statements in the area of my math calcculation, but i get an error that says the aButton etc. cannot be found. I thought this might work if the variables were updated just before doing the calculation. I am having a second problem with my calculation. Although the math was working correctly when I got input from the user in the previous version, it looks like when I assign the variables directly I am getting the wrong answer. Anyway, if I can get some help with the radio buttons, I can work on figuring out the problem with the math.
Any aqssistance would be greatly appreciated.

My code is below.

/* Mortgage Monyhly Payment Calculator with graphical user interface
Programmer:  J.Schab
Date:        June 4,2006
Purpose:     This project accepts the mortgage amount and gives the user a choice of 3 loan types through the use of radio buttons. The program then calculates the monthly mortgage payment and displays it in currency format.
There is a quit button to exit the application, and a clear button to clear user entered fields in order to calculate a new mortgage. The program will also clear the payment field should the user press any key while positioned
in any input textfield.


import javax.swing.*;
import javax.swing.border.*;
import javax.swing.JScrollPane.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.event.*;
import java.text.NumberFormat;
import java.util.Locale;
import java.text.*;

class Mortgage extends JFrame

     int term = 0;
     double yearlyRate = 0.00;        

    private JLabel headerJLabel;

    Border rowborder = new EmptyBorder( 3, 10, 3, 10 );
    String titles = "Month \t Principal\t Interest\tBalance\n";        

    // JLabel and JTextField for the mortgage amount
    private JLabel amountJLabel;
    private JTextField amountJTextField;

    // JLabel for monthly mortgage payment
    private JLabel monthpayJLabel;

    // JTextArea for displaying payment
    private JTextArea outputJTextArea;

    // JButton to initiate calculations
    private JButton calculateJButton;

    // JButton to clear entries
    private JButton clearJButton;

    // JButton to quit
    private JButton quitJButton;

    // no-argument constructor    
    public Mortgage()


    // create and position the GUI components; register event handlers
    private void createUserInterface()
        // get content pane for attaching GUI components
        Container contentPane = getContentPane();

        JTextArea displayArea = new JTextArea(10, 45);
        JScrollPane scroll = new JScrollPane(displayArea);

        setTitle("Mortgage Calculator"); // set title bar text

        // set northLabel using borderlayout
        headerJLabel = new JLabel();
        headerJLabel.setBounds(10, 1, 300, 46);
        headerJLabel.setText("Enter a mortgage amount and select a loan");

        // enable specific positioning of GUI components

        // set up amountJLabel
        amountJLabel = new JLabel();
        amountJLabel.setBounds(76, 36, 104, 26);
        amountJLabel.setText("Mortgage amount:");

        // set up amountJTextField
        amountJTextField = new JTextField();
        amountJTextField.setBounds(200, 36, 56, 26);

        new KeyAdapter() // anonymous inner class
            // event handler for key pressed in amountJTextField
            public void keyPressed(KeyEvent event)

        } // end anonymous inner class

        ); // end call to addKeyListener

    // added code below for radio buttons

        JPanel radioPanel = new JPanel();
               JRadioButton aButton = new JRadioButton("7 Years at 5.35%" , true);
               JRadioButton bButton = new JRadioButton("15 Years at 5.50%" , false);
               JRadioButton cButton = new JRadioButton("30 Years at 5.75%", false);

        ButtonGroup bgroup = new ButtonGroup();      
          radioPanel.setLayout(new FlowLayout(FlowLayout.LEFT, 4, 4 ));      
          //radioPanel.setMaximumSize( new Dimension( 10000, radioPanel.getMinimumSize().height ) );
          radioPanel.setBorder( rowborder );
          radioPanel.setBounds( 90, 56, 195, 95 );
          if (aButton.isSelected()){
             term = 7;
             yearlyRate = 5.35;
          if (bButton.isSelected()){
             term = 15;
             yearlyRate = 5.50;
          if (cButton.isSelected()){
             term = 30;
             yearlyRate = 5.75;

        // set up calculateJButton
        calculateJButton = new JButton();
        calculateJButton.setBounds(26, 320, 90, 26);

        new ActionListener() // anonymous inner class
            // event handler called when calculateJButton is pressed
            public void actionPerformed(ActionEvent event)

        } // end anonymous inner class

        ); // end call to addActionListener

        // set up clearJButton
        clearJButton = new JButton();
        clearJButton.setBounds(136, 320, 90, 26);

        new ActionListener() // anonymous inner class
            // event handler called when clearJButton is pressed
            public void actionPerformed(ActionEvent event)

        } // end anonymous inner class

        ); // end call to addActionListener

        // set up quitJButton
        quitJButton = new JButton();
        quitJButton.setBounds(250, 320, 90, 26);

        new ActionListener() // anonymous inner class
            // event handler called when quitJButton is pressed
            public void actionPerformed(ActionEvent event)

        } // end anonymous inner class

        ); // end call to addActionListener

        // set up outputJTextArea
        outputJTextArea = new JTextArea();
        outputJTextArea.setBounds(200, 146, 56, 26);

        //set up monthpayJLabel
        monthpayJLabel = new JLabel();
        monthpayJLabel.setBounds(76, 146, 156, 26);
        monthpayJLabel.setText("Monthly Payment:");

        scroll.setBounds(20, 186, 356, 130);

    } // end method createUserInterface

    // called when user presses key in amountJTextField
    private void amountJTextFieldkeyPressed(KeyEvent event)
        outputJTextArea.setText(""); // clear outputJTextArea

        // method called when user clicks calculateJButton
    private void calculateJButtonActionPerformed(ActionEvent event)
            //int term = Integer.parseInt(termJTextField.getText());
                // length of the loan in years
            int monthCount = (term * 12); // Calculate months from years
            int amount = Integer.parseInt(amountJTextField.getText());
            //double yearlyRate = Double.parseDouble(interestJTextField.getText())
            //    ;
            double interestRateMonthly = (yearlyRate / 12) / 100;
                // Calculate monthly interest
            double monthlyPayment; // monthly payment amount variable

            // Calculate monthly payment
            monthlyPayment = (amount * interestRateMonthly) / (1-Math.pow(1 +
                interestRateMonthly,  - monthCount));

            DecimalFormat currency = new DecimalFormat("$0.00");
                // Format output
                // Output payment amount

        catch (NumberFormatException ex){}

    // method called when user clicks clearJButton
    private void clearJButtonActionPerformed(ActionEvent event)
            outputJTextArea.setText(""); // clear outputJTextArea
            amountJTextField.setText(""); // clear amountJTextField
            //interestJTextField.setText(""); // clear interestJTextField
            //termJTextField.setText(""); // clear termJTextField

        catch (NumberFormatException ex){}

    // method called when user clicks quitJButton
    private void quitJButtonActionPerformed(ActionEvent event)

        catch (NumberFormatException ex){}

    // main method
    public static void main(String[]args)
        Mortgage application = new Mortgage();
        application.setSize(400, 400);
    } // end method main

} // end class Mortgage
Question by:ghost8067
  • 2
LVL 24

Accepted Solution

sciuriware earned 500 total points
ID: 16877066
              JRadioButton aButton = new JRadioButton("7 Years at 5.35%" , true);
               JRadioButton bButton = new JRadioButton("15 Years at 5.50%" , false);
               JRadioButton cButton = new JRadioButton("30 Years at 5.75%", false);

These buttons are local to
               private void createUserInterface()

So they will disappear upon return and can't be accessed from outside.

Add them to the other buttons.


Author Comment

ID: 16877236
Thanks so much for the help. It is working like a charm. This also corrected the math issue.
Have a great day.
LVL 24

Expert Comment

ID: 16877357
At your service; success with your study.


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