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"Java@Work: Old Places, Old Faces"
by Al Williams
Web Techniques, January 1999

Web Techniques grants permission to use these listings (and code) for 
private or commercial use provided that credit to Web Techniques and 
the author is maintained within the comments of the source. For 
questions, contact editors@web-techniques.com. 



[LISTING ONE]


//Title:       Mortgage Calculator
//Version:
//Copyright:   Copyright (c) 1998
//Author:      Al Williams
//Company:     AWC
//Description: This is a mortgage calculator applet
//created with JBuilder
package mcalc;

import java.awt.*;
import java.awt.event.*;
import java.applet.*;
import com.sun.java.swing.*;
import java.text.NumberFormat;
import java.text.ParseException;
import borland.jbcl.layout.*;

public class Mcalc extends JApplet {
  boolean isStandalone = false;
  TextField Principal = new TextField();
  Label label1 = new Label();
  XYLayout xYLayout1 = new XYLayout();
  TextField Rate = new TextField();
  Label label2 = new Label();
  TextField Months = new TextField();
  Label label3 = new Label();
  Button Calc = new Button();
  Label Payment = new Label();
  Label Total = new Label();
//Get a parameter value

  public String getParameter(String key, String def) {
    return isStandalone ? System.getProperty(key, def) :
      (getParameter(key) != null ? getParameter(key) : def);
  }

  //Construct the applet

  public Mcalc() {
  }
//Initialize the applet

  public void init() {
    try {
    jbInit();
    }
    catch (Exception e) {
    e.printStackTrace();
    }
  }

//Component initialization

  private void jbInit() throws Exception {
    this.getContentPane().setLayout(xYLayout1);
    label1.setText("Principal:");
    xYLayout1.setHeight(300);
    xYLayout1.setWidth(313);
    label2.setText("Interest Rate:");
    label3.setText("Months:");
    Calc.setLabel("Calculate");
    Calc.addActionListener(new java.awt.event.ActionListener() {
      public void actionPerformed(ActionEvent e) {
        Calc_actionPerformed(e);
      }
    });
    this.setSize(400,300);
    this.getContentPane().add(Principal, 
      new XYConstraints(103, 16, 183, -1));
    this.getContentPane().add(label1, 
      new XYConstraints(9, 16, -1, -1));
    this.getContentPane().add(Rate, 
      new XYConstraints(104, 58, 183, -1));
    this.getContentPane().add(label2, 
      new XYConstraints(9, 60, -1, -1));
    this.getContentPane().add(Months, 
      new XYConstraints(106, 102, 183, -1));
    this.getContentPane().add(label3, 
      new XYConstraints(11, 104, -1, -1));
    this.getContentPane().add(Calc, 
      new XYConstraints(121, 158, 80, 34));
    this.getContentPane().add(Payment, 
      new XYConstraints(18, 214, 142, -1));
    this.getContentPane().add(Total, 
      new XYConstraints(19, 240, 142, -1));
  }
//Start the applet

  public void start() {
  }
//Stop the applet

  public void stop() {
  }
//Destroy the applet

  public void destroy() {
  }
//Get Applet information

  public String getAppletInfo() {
    return "Mortgage Calculator by Al Williams";
  }
//Get parameter info

  public String[][] getParameterInfo() {
    return null;
  }
//Main method

  public static void main(String[] args) {
    Mcalc applet = new Mcalc();
    applet.isStandalone = true;
    JFrame frame = new JFrame();
    frame.setTitle("Mortgage Calculator");
    frame.getContentPane().add(applet, BorderLayout.CENTER);
    applet.init();
    applet.start();
    frame.setSize(400,320);
    Dimension d = Toolkit.getDefaultToolkit().getScreenSize();
    frame.setLocation((d.width - frame.getSize().width) /
       2, (d.height - frame.getSize().height) / 2);
    frame.setVisible(true);
  }

  void Calc_actionPerformed(ActionEvent e) {
    float intrate, amt;
    int period;
    float intpermonth;
    float pmt,total;
    double factor;
    NumberFormat fmt = NumberFormat.getCurrencyInstance();
    NumberFormat gfmt = NumberFormat.getInstance();
    // read inputs
    intrate= 0.0f;
    try
      {
      intrate=gfmt.parse(Rate.getText()).floatValue()/100.0f;
      }
    catch (ParseException ex)
      {
      Payment.setText("Bad period");
      return;
      }
    period=Integer.parseInt(Months.getText());
    amt=0.0f;
    try
      {
      amt=gfmt.parse(Principal.getText()).floatValue();
      }
    catch (ParseException ex)
      {
      Payment.setText("Bad amount");
      return;
      }

    // calculate
    intpermonth=intrate/12;
    factor=Math.exp(-period* Math.log(1.0+intpermonth));
    pmt=(float)(amt*intpermonth/(1.0-factor));
    total=pmt*period;

    // set outputs -- use NumberFormat to format numbers
    Payment.setText("Payment = " + fmt.format(pmt));
    Total.setText("Total = " + fmt.format(total));
  }
}