Java Program to Calculate Initial Investment for Desired Annuity

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.text.*;
/*


*/
public class Annuity extends JApplet
implements ActionListener {
JTextField regWDText, initialText, periodText,
rateText, numWDText;
JButton doIt;
double regWDAmount;
double rateOfRet;
double numYears;
int numPerYear;
NumberFormat nf;
public void init() {
try {
SwingUtilities.invokeAndWait(new Runnable () {
public void run() {
makeGUI();
}
});
} catch(Exception exc) {
System.out.println("Can't create because of "+ exc);
}
}
private void makeGUI() {
GridBagLayout gbag = new GridBagLayout();
GridBagConstraints gbc = new GridBagConstraints();
setLayout(gbag);
JLabel heading = new
JLabel("Initial Investment Needed for " +
"Regular Withdrawals");
JLabel regWDLab = new JLabel("Desired Withdrawal ");
JLabel periodLab = new JLabel("Years ");
JLabel rateLab = new JLabel("Rate of Return ");
JLabel numWDLab =
new JLabel("Number of Withdrawals per Year ");
JLabel initialLab =
new JLabel("Initial Investment Required ");
regWDText = new JTextField(10);
periodText = new JTextField(10);
initialText = new JTextField(10);
rateText = new JTextField(10);
numWDText = new JTextField(10);
initialText.setEditable(false);
doIt = new JButton("Compute");
gbc.weighty = 1.0;
gbc.gridwidth = GridBagConstraints.REMAINDER;
gbc.anchor = GridBagConstraints.NORTH;
gbag.setConstraints(heading, gbc);
gbc.anchor = GridBagConstraints.EAST;
gbc.gridwidth = GridBagConstraints.RELATIVE;
gbag.setConstraints(regWDLab, gbc);
gbc.gridwidth = GridBagConstraints.REMAINDER;
gbag.setConstraints(regWDText, gbc);
gbc.gridwidth = GridBagConstraints.RELATIVE;
gbag.setConstraints(periodLab, gbc);
gbc.gridwidth = GridBagConstraints.REMAINDER;
gbag.setConstraints(periodText, gbc);
gbc.gridwidth = GridBagConstraints.RELATIVE;
gbag.setConstraints(rateLab, gbc);
gbc.gridwidth = GridBagConstraints.REMAINDER;
gbag.setConstraints(rateText, gbc);
gbc.gridwidth = GridBagConstraints.RELATIVE;
gbag.setConstraints(numWDLab, gbc);
gbc.gridwidth = GridBagConstraints.REMAINDER;
gbag.setConstraints(numWDText, gbc);
gbc.gridwidth = GridBagConstraints.RELATIVE;
gbag.setConstraints(initialLab, gbc);
gbc.gridwidth = GridBagConstraints.REMAINDER;
gbag.setConstraints(initialText, gbc);
gbc.anchor = GridBagConstraints.CENTER;
gbag.setConstraints(doIt, gbc);
add(heading);
add(regWDLab);
add(regWDText);
add(periodLab);
add(periodText);
add(rateLab);
add(rateText);
add(numWDLab);
add(numWDText);
add(initialLab);
add(initialText);
add(doIt);
regWDText.addActionListener(this);
periodText.addActionListener(this);
rateText.addActionListener(this);
numWDText.addActionListener(this);
doIt.addActionListener(this);
nf = NumberFormat.getInstance();
nf.setMinimumFractionDigits(2);
nf.setMaximumFractionDigits(2);
}
public void actionPerformed(ActionEvent ae) {
double result = 0.0;
String regWDStr = regWDText.getText();
String periodStr = periodText.getText();
String rateStr = rateText.getText();
String numWDStr = numWDText.getText();
try {
if(regWDStr.length() != 0 &&
periodStr.length() != 0 &&
rateStr.length() != 0 &&
numWDStr.length() != 0) {
regWDAmount = Double.parseDouble(regWDStr);
numYears = Double.parseDouble(periodStr);
rateOfRet = Double.parseDouble(rateStr) / 100;
numPerYear = Integer.parseInt(numWDStr);
result = compute();
initialText.setText(nf.format(result));
}
showStatus("");
} catch (NumberFormatException exc) {
showStatus("Invalid Data");
initialText.setText("");
}
}
double compute() {
double b, e;
double t1, t2;
t1 = (regWDAmount * numPerYear) / rateOfRet;
b = (1 + rateOfRet/numPerYear);
e = numPerYear * numYears;
t2 = 1 - (1 / Math.pow(b, e));
return t1 * t2;
}
}