Java applet program (together with its html test file) to calculate loan payments.

[mike saggese]

hi, I need help with a new assignment. I have to write a Java applet program (together with its html test file) to calculate loan payments. The user will provide the interest rate, the number of years, and loan amount

this is what I have so far

package components;

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.text.*;
import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeEvent;
import java.text.*;


public class LoanCalculator extends JPanel
                                    implements PropertyChangeListener {
    //Values for the fields
    private double amount = 100000;
    private double rate = 7.5;  //7.5%
    private int numPeriods = 30;

    //Labels to identify the fields
    private JLabel amountLabel;
    private JLabel rateLabel;
    private JLabel numPeriodsLabel;
    private JLabel paymentLabel;

    //Strings for the labels
    private static String amountString = "Loan Amount: ";
    private static String rateString = "APR (%): ";
    private static String numPeriodsString = "Years: ";
    private static String paymentString = "Monthly Payment: ";

    //Fields for data entry
    private JFormattedTextField amountField;
    private JFormattedTextField rateField;
    private JFormattedTextField numPeriodsField;
    private JFormattedTextField paymentField;

    //Formats to format and parse numbers
    private NumberFormat amountFormat;
    private NumberFormat percentFormat;
    private NumberFormat paymentFormat;

    public LoanCalculator() {
        super(new BorderLayout());
        setUpFormats();
        double payment = computePayment(amount,
                                        rate,
                                        numPeriods);

        //Create the labels.
        amountLabel = new JLabel(amountString);
        rateLabel = new JLabel(rateString);
        numPeriodsLabel = new JLabel(numPeriodsString);
        paymentLabel = new JLabel(paymentString);

        //Create the text fields and set them up.
        amountField = new JFormattedTextField(amountFormat);
        amountField.setValue(new Double(amount));
        amountField.setColumns(10);
        amountField.addPropertyChangeListener("value", this);

        rateField = new JFormattedTextField(percentFormat);
        rateField.setValue(new Double(rate));
        rateField.setColumns(10);
        rateField.addPropertyChangeListener("value", this);

        numPeriodsField = new JFormattedTextField();
        numPeriodsField.setValue(new Integer(numPeriods));
        numPeriodsField.setColumns(10);
        numPeriodsField.addPropertyChangeListener("value", this);

        paymentField = new JFormattedTextField(paymentFormat);
        paymentField.setValue(new Double(payment));
        paymentField.setColumns(10);
        paymentField.setEditable(false);
        paymentField.setForeground(Color.red);

        //Tell accessibility tools about label/textfield pairs.
        amountLabel.setLabelFor(amountField);
        rateLabel.setLabelFor(rateField);
        numPeriodsLabel.setLabelFor(numPeriodsField);
        paymentLabel.setLabelFor(paymentField);

        //Lay out the labels in a panel.
        JPanel labelPane = new JPanel(new GridLayout(0,1));
        labelPane.add(amountLabel);
        labelPane.add(rateLabel);
        labelPane.add(numPeriodsLabel);
        labelPane.add(paymentLabel);

        //Layout the text fields in a panel.
        JPanel fieldPane = new JPanel(new GridLayout(0,1));
        fieldPane.add(amountField);
        fieldPane.add(rateField);
        fieldPane.add(numPeriodsField);
        fieldPane.add(paymentField);

        //Put the panels in this panel, labels on left,
        //text fields on right.
        setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
        add(labelPane, BorderLayout.CENTER);
        add(fieldPane, BorderLayout.LINE_END);
    }

    /** Called when a field's "value" property changes. */
    public void propertyChange(PropertyChangeEvent e) {
        Object source = e.getSource();
        if (source == amountField) {
            amount = ((Number)amountField.getValue()).doubleValue();
        } else if (source == rateField) {
            rate = ((Number)rateField.getValue()).doubleValue();
        } else if (source == numPeriodsField) {
            numPeriods = ((Number)numPeriodsField.getValue()).intValue();
        }

        double payment = computePayment(amount, rate, numPeriods);
        paymentField.setValue(new Double(payment));
    }

    /**
     * Create the GUI and show it.  For thread safety,
     * this method should be invoked from the
     * event dispatch thread.
     */
    private static void createAndShowGUI() {
        //Create and set up the window.
        JFrame frame = new JFrame("LoanCalculator");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        //Add contents to the window.
        frame.add(new LoanCalculator());

        //Display the window.
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        //Schedule a job for the event dispatch thread:
        //creating and showing this application's GUI.
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                //Turn off metal's use of bold fonts
	        UIManager.put("swing.boldMetal", Boolean.FALSE);
                createAndShowGUI();
            }
        });
    }

    //Compute the monthly payment based on the loan amount,
    //APR, and length of loan.
    double computePayment(double loanAmt, double rate, int numPeriods) {
        double I, partial1, denominator, answer;

        numPeriods *= 12;        //get number of months
        if (rate > 0.01) {
            I = rate / 100.0 / 12.0;         //get monthly rate from annual
            partial1 = Math.pow((1 + I), (0.0 - numPeriods));
            denominator = (1 - partial1) / I;
        } else { //rate ~= 0
            denominator = numPeriods;
        }

        answer = (-1 * loanAmt) / denominator;
        return answer;
    }

    //Create and set up number formats. These objects also
    //parse numbers input by user.
    private void setUpFormats() {
        amountFormat = NumberFormat.getNumberInstance();

        percentFormat = NumberFormat.getNumberInstance();
        percentFormat.setMinimumFractionDigits(3);

        paymentFormat = NumberFormat.getCurrencyInstance();
    }
}

if anyone can help me that would be great. thank you

[Steve Luke]

mike saggese wrote:hi, I need help with a new assignment. I have to write a Java applet program (together with its html test file) to calculate loan payments. The user will provide the interest rate, the number of years, and loan amount

this is what I have so far

way too much code to go through

if anyone can help me that would be great. thank you

Do you have a question?

[mike saggese]

Steve Luke wrote:

mike saggese wrote:hi, I need help with a new assignment. I have to write a Java applet program (together with its html test file) to calculate loan payments. The user will provide the interest rate, the number of years, and loan amount

this is what I have so far

way too much code to go through

if anyone can help me that would be great. thank you

Do you have a question?

yes actually. I was trying to write a java loan calculator applet and I'm having some trouble. here's my code

import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.Label;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JApplet;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.border.TitledBorder;


public class LoanCalculator extends JApplet
implements ActionListener
{
private JTextField jtfInterestRate = new JTextField(10);
private JTextField jtfYear = new JTextField(10);
private JTextField jtfLoan = new JTextField(10);
private JTextField jtfMonthlyPay = new JTextField(10);
private JTextField jtfTotalPay = new JTextField(10);

private JButton jbtCompute = new JButton("Compute Payment");

public LoanCalculator()
{
this.jtfMonthlyPay.setEditable(false);
this.jtfTotalPay.setEditable(false);

this.jtfInterestRate.setHorizontalAlignment(4);
this.jtfYear.setHorizontalAlignment(4);
this.jtfLoan.setHorizontalAlignment(4);
this.jtfMonthlyPay.setHorizontalAlignment(4);
this.jtfTotalPay.setHorizontalAlignment(4);

JPanel p1 = new JPanel();
p1.setLayout(new GridLayout(5, 2));
p1.add(new Label("Interest Rate (e.g., 5.5 for 5.5%)"));
p1.add(this.jtfInterestRate);
p1.add(new Label("Years "));
p1.add(this.jtfYear);
p1.add(new Label("Loan Amount"));
p1.add(this.jtfLoan);
p1.add(new Label("Monthly Payment"));
p1.add(this.jtfMonthlyPay);
p1.add(new Label("Total Payment"));
p1.add(this.jtfTotalPay);
p1.setBorder(new TitledBorder(
"Enter interest rate, year and loan amount"));

JPanel p2 = new JPanel();
p2.setLayout(new FlowLayout(2));
p2.add(this.jbtCompute);

add(p1, "Center");
add(p2, "South");

this.jbtCompute.addActionListener(this);
}

public void actionPerformed(ActionEvent e)
{
if (e.getSource() == this.jbtCompute)
{
double interest =
Double.valueOf(this.jtfInterestRate.getText()).doubleValue();
int year =
Integer.valueOf(this.jtfYear.getText()).intValue();
double loanAmount =
Double.valueOf(this.jtfLoan.getText()).doubleValue();

Loan loan = new Loan(interest, year, loanAmount);

this.jtfMonthlyPay.setText(String.format("%.2f", new Object[] { Double.valueOf(loan.getMonthlyPayment()) }));
this.jtfTotalPay.setText(String.format("%.2f", new Object[] { Double.valueOf(loan.getTotalPayment()) }));
}
}

public static void main(String[] args)
{
JFrame frame = new JFrame("Loan Calulator");

LoanCalculator applet = new LoanCalculator();

frame.add(applet, "Center");

applet.init();
applet.start();

frame.setSize(350, 250);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
}

tried
At line 72 the error is that it cannot find symbol. its where the Loan loan = new Loan(interest, year, loanAmount); is. I've tried adding public class loan and that didn't work. I've tried the no class found def exception and that didn't work either. I also know that Nothing in the above code indicates that I actually have a Loan class. Is this a different package and I'm just missing an import. Any help would be great. thanks