Implement a mortgage calculator with four JFormattedTextFields in Java

/*//w  w w .ja  v a2s .co m
 * Copyright (c) 1995 - 2008 Sun Microsystems, Inc.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Sun Microsystems nor the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.GridLayout;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.text.NumberFormat;

import javax.swing.BorderFactory;
import javax.swing.JFormattedTextField;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;

/**
 * FormattedTextFieldDemo.java requires no other files.
 * 
 * It implements a mortgage calculator that uses four JFormattedTextFields.
 */
public class Main 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 Main() {
    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("FormattedTextFieldDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

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

    // 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();
  }
}