Input Verification Demo
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/*
* InputVerificationDemo.java is a 1.4 example that
* requires no other files.
*/
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.GridLayout;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.DecimalFormat;
import java.text.NumberFormat;
import java.text.ParseException;
import javax.swing.BorderFactory;
import javax.swing.InputVerifier;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
/**
* InputVerificationDemo.java is a 1.4 example that requires no other files.
*
* Yet another mortgage calculator. However, instead of using a formatted text
* field, as shown in FormattedTextFieldDemo, this example uses input
* verification to validate user input.
*/
public class InputVerificationDemo extends JPanel {
//Default values
private static double DEFAULT_AMOUNT = 100000;
private static double DEFAULT_RATE = 7.5; //7.5%
private static int DEFAULT_PERIOD = 30;
//Labels to identify the text fields
private JLabel amountLabel;
private JLabel rateLabel;
private JLabel numPeriodsLabel;
private JLabel paymentLabel;
//Strings for the labels
private static String amountString = "Loan Amount (10,000-10,000,000): ";
private static String rateString = "APR (>= 0%): ";
private static String numPeriodsString = "Years (1-40): ";
private static String paymentString = "Monthly Payment: ";
//Text fields for data entry
private JTextField amountField;
private JTextField rateField;
private JTextField numPeriodsField;
private JTextField paymentField;
//Formats to format and parse numbers
private NumberFormat moneyFormat;
private NumberFormat percentFormat;
private DecimalFormat decimalFormat;
private DecimalFormat paymentFormat;
private MyVerifier verifier = new MyVerifier();
public InputVerificationDemo() {
super(new BorderLayout());
setUpFormats();
double payment = computePayment(DEFAULT_AMOUNT, DEFAULT_RATE,
DEFAULT_PERIOD);
//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 JTextField(moneyFormat.format(DEFAULT_AMOUNT), 10);
amountField.setInputVerifier(verifier);
rateField = new JTextField(percentFormat.format(DEFAULT_RATE), 10);
rateField.setInputVerifier(verifier);
numPeriodsField = new JTextField(decimalFormat.format(DEFAULT_PERIOD),
10);
numPeriodsField.setInputVerifier(verifier);
paymentField = new JTextField(paymentFormat.format(payment), 10);
paymentField.setInputVerifier(verifier);
paymentField.setEditable(false);
//Remove this component from the focus cycle.
paymentField.setFocusable(false);
paymentField.setForeground(Color.red);
//Register an action listener to handle Return.
amountField.addActionListener(verifier);
rateField.addActionListener(verifier);
numPeriodsField.addActionListener(verifier);
//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);
}
class MyVerifier extends InputVerifier implements ActionListener {
double MIN_AMOUNT = 10000.0;
double MAX_AMOUNT = 10000000.0;
double MIN_RATE = 0.0;
int MIN_PERIOD = 1;
int MAX_PERIOD = 40;
public boolean shouldYieldFocus(JComponent input) {
boolean inputOK = verify(input);
makeItPretty(input);
updatePayment();
if (inputOK) {
return true;
} else {
Toolkit.getDefaultToolkit().beep();
return false;
}
}
protected void updatePayment() {
double amount = DEFAULT_AMOUNT;
double rate = DEFAULT_RATE;
int numPeriods = DEFAULT_PERIOD;
double payment = 0.0;
//Parse the values.
try {
amount = moneyFormat.parse(amountField.getText()).doubleValue();
} catch (ParseException pe) {
}
try {
rate = percentFormat.parse(rateField.getText()).doubleValue();
} catch (ParseException pe) {
}
try {
numPeriods = decimalFormat.parse(numPeriodsField.getText())
.intValue();
} catch (ParseException pe) {
}
//Calculate the result and update the GUI.
payment = computePayment(amount, rate, numPeriods);
paymentField.setText(paymentFormat.format(payment));
}
//This method checks input, but should cause no side effects.
public boolean verify(JComponent input) {
return checkField(input, false);
}
protected void makeItPretty(JComponent input) {
checkField(input, true);
}
protected boolean checkField(JComponent input, boolean changeIt) {
if (input == amountField) {
return checkAmountField(changeIt);
} else if (input == rateField) {
return checkRateField(changeIt);
} else if (input == numPeriodsField) {
return checkNumPeriodsField(changeIt);
} else {
return true; //shouldn't happen
}
}
//Checks that the amount field is valid. If it is valid,
//it returns true; otherwise, returns false. If the
//change argument is true, this method reigns in the
//value if necessary and (even if not) sets it to the
//parsed number so that it looks good -- no letters,
//for example.
protected boolean checkAmountField(boolean change) {
boolean wasValid = true;
double amount = DEFAULT_AMOUNT;
//Parse the value.
try {
amount = moneyFormat.parse(amountField.getText()).doubleValue();
} catch (ParseException pe) {
wasValid = false;
}
//Value was invalid.
if ((amount < MIN_AMOUNT) || (amount > MAX_AMOUNT)) {
wasValid = false;
if (change) {
if (amount < MIN_AMOUNT) {
amount = MIN_AMOUNT;
} else { // amount is greater than MAX_AMOUNT
amount = MAX_AMOUNT;
}
}
}
//Whether value was valid or not, format it nicely.
if (change) {
amountField.setText(moneyFormat.format(amount));
amountField.selectAll();
}
return wasValid;
}
//Checks that the rate field is valid. If it is valid,
//it returns true; otherwise, returns false. If the
//change argument is true, this method reigns in the
//value if necessary and (even if not) sets it to the
//parsed number so that it looks good -- no letters,
//for example.
protected boolean checkRateField(boolean change) {
boolean wasValid = true;
double rate = DEFAULT_RATE;
//Parse the value.
try {
rate = percentFormat.parse(rateField.getText()).doubleValue();
} catch (ParseException pe) {
wasValid = false;
}
//Value was invalid.
if (rate < MIN_RATE) {
wasValid = false;
if (change) {
rate = MIN_RATE;
}
}
//Whether value was valid or not, format it nicely.
if (change) {
rateField.setText(percentFormat.format(rate));
rateField.selectAll();
}
return wasValid;
}
//Checks that the numPeriods field is valid. If it is valid,
//it returns true; otherwise, returns false. If the
//change argument is true, this method reigns in the
//value if necessary and (even if not) sets it to the
//parsed number so that it looks good -- no letters,
//for example.
protected boolean checkNumPeriodsField(boolean change) {
boolean wasValid = true;
int numPeriods = DEFAULT_PERIOD;
//Parse the value.
try {
numPeriods = decimalFormat.parse(numPeriodsField.getText())
.intValue();
} catch (ParseException pe) {
wasValid = false;
}
//Value was invalid.
if ((numPeriods < MIN_PERIOD) || (numPeriods > MAX_PERIOD)) {
wasValid = false;
if (change) {
if (numPeriods < MIN_PERIOD) {
numPeriods = MIN_PERIOD;
} else { // numPeriods is greater than MAX_PERIOD
numPeriods = MAX_PERIOD;
}
}
}
//Whether value was valid or not, format it nicely.
if (change) {
numPeriodsField.setText(decimalFormat.format(numPeriods));
numPeriodsField.selectAll();
}
return wasValid;
}
public void actionPerformed(ActionEvent e) {
JTextField source = (JTextField) e.getSource();
shouldYieldFocus(source); //ignore return value
source.selectAll();
}
}
/**
* Create the GUI and show it. For thread safety, this method should be
* invoked from the event-dispatching thread.
*/
private static void createAndShowGUI() {
//Make sure we have nice window decorations.
JFrame.setDefaultLookAndFeelDecorated(true);
//Create and set up the window.
JFrame frame = new JFrame("InputVerificationDemo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Create and set up the content pane.
JComponent newContentPane = new InputVerificationDemo();
newContentPane.setOpaque(true); //content panes must be opaque
frame.setContentPane(newContentPane);
//Display the window.
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
//Schedule a job for the event-dispatching thread:
//creating and showing this application's GUI.
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
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 are used
//for both parsing input and formatting output.
private void setUpFormats() {
moneyFormat = (NumberFormat) NumberFormat.getNumberInstance();
percentFormat = NumberFormat.getNumberInstance();
percentFormat.setMinimumFractionDigits(3);
decimalFormat = (DecimalFormat) NumberFormat.getNumberInstance();
decimalFormat.setParseIntegerOnly(true);
paymentFormat = (DecimalFormat) NumberFormat.getNumberInstance();
paymentFormat.setMaximumFractionDigits(2);
paymentFormat.setNegativePrefix("(");
paymentFormat.setNegativeSuffix(")");
}
}
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