Java The Complete Reference, Seventh Edition

934 Part IV: Applying Java

gbc.gridwidth = GridBagConstraints.REMAINDER;

gbag.setConstraints(paymentText, gbc);

gbc.anchor = GridBagConstraints.CENTER;

gbag.setConstraints(doIt, gbc);

// Add all the components.

add(heading);

add(amountLab);

add(amountText);

add(periodLab);

add(periodText);

add(rateLab);

add(rateText);

add(paymentLab);

add(paymentText);

add(doIt);

// Register to receive action events.

amountText.addActionListener(this);

periodText.addActionListener(this);

rateText.addActionListener(this);

doIt.addActionListener(this);

// Create a number format.

nf = NumberFormat.getInstance();

nf.setMinimumFractionDigits(2);

nf.setMaximumFractionDigits(2);

}

/* User pressed Enter on a text field or

pressed Compute. Display the result if all

fields are completed. */

public void actionPerformed(ActionEvent ae) {

double result = 0.0;

String amountStr = amountText.getText();

String periodStr = periodText.getText();

String rateStr = rateText.getText();

try {

if(amountStr.length() != 0 &&

periodStr.length() != 0 &&

rateStr.length() != 0) {

principal = Double.parseDouble(amountStr);

numYears = Double.parseDouble(periodStr);

intRate = Double.parseDouble(rateStr) / 100;

result = compute();

paymentText.setText(nf.format(result));

}

showStatus(""); // erase any previous error message