import java.awt.*;
import java.awt.event.*;

import com.sun.java.swing.*; 
import com.sun.java.swing.event.*; 
import com.sun.java.swing.text.*; 

import java.text.*; 
import java.util.Locale; 

public class TextFieldDemo extends JFrame {

    //Values for the text fields
    private double amount = 100000;
    private double rate = .075;
    private int numPeriods = 30;
    private double payment = 0.0;

    //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: ";
    private static String rateString = "APR: ";
    private static String numPeriodsString = "Years: ";
    private static String paymentString = "Monthly Payment: ";

    //Text fields for data entry
    private DecimalField amountField;
    private DecimalField rateField;
    private WholeNumberField numPeriodsField;
    private DecimalField paymentField;

    //Formats to format and parse numbers
    private NumberFormat moneyFormat;
    private NumberFormat percentFormat;

    public TextFieldDemo() {
        super("TextFieldDemo");

        setUpFormats();

	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
	MyDocumentListener myDocumentListener = new MyDocumentListener();

        amountField = new DecimalField(amount, 10, moneyFormat);
	amountField.getDocument().addDocumentListener(myDocumentListener);
	amountField.getDocument().putProperty("name", "amount");

        rateField = new DecimalField(rate, 10, percentFormat);
	rateField.getDocument().addDocumentListener(myDocumentListener);
	rateField.getDocument().putProperty("name", "rate");

        numPeriodsField = new WholeNumberField(numPeriods, 10);
	numPeriodsField.getDocument().addDocumentListener(myDocumentListener);
	numPeriodsField.getDocument().putProperty("name", "numPeriods");

        paymentField = new DecimalField(payment, 10, moneyFormat);
        paymentField.setEditable(false);
        paymentField.setForeground(Color.red);

	//Layout the labels in a panel
        JPanel labelPane = new JPanel();
        labelPane.setLayout(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();
        fieldPane.setLayout(new GridLayout(0, 1));
        fieldPane.add(amountField);
        fieldPane.add(rateField);
        fieldPane.add(numPeriodsField);
        fieldPane.add(paymentField);

	//Put the panels in another panel, labels on left,
	//text fields on right
	JPanel contentPane = new JPanel();
        contentPane.setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
        contentPane.setLayout(new BorderLayout());
	contentPane.add(labelPane);
	contentPane.add(fieldPane, "East");

        setContentPane(contentPane);
    }

    class MyDocumentListener implements DocumentListener {
	public void insertUpdate(DocumentEvent e) {
	    update(e);
	}
	public void removeUpdate(DocumentEvent e) {
	    update(e);
	}
	public void changedUpdate(DocumentEvent e) {
	    // we won't ever get this with PlainDocument
	}
	private void update(DocumentEvent e) {
	    Document whatsup = e.getDocument();
	    if (whatsup.getProperty("name").equals("amount"))
		amount = amountField.getValue();
	    else if (whatsup.getProperty("name").equals("rate"))
		rate = rateField.getValue();
	    else if (whatsup.getProperty("name").equals("numPeriods"))
		numPeriods = numPeriodsField.getValue();
	    payment = computePayment(amount, rate, numPeriods);
	    paymentField.setValue(payment);
	}
    }

    public static void main(String[] args) {
        JFrame frame = new TextFieldDemo();

        WindowListener l = new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        };
        frame.addWindowListener(l);

        frame.pack();
        frame.setVisible(true);
    }

    //Computes 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;

        I = rate / 12.0;         // get monthly rate from annual
        numPeriods *= 12;        // get number of months
        partial1 = Math.pow((1 + I), (0.0 - numPeriods));
        denominator = (1 - partial1) / I;
        answer = (-1 * loanAmt) / denominator;
        return answer;
    }

    // create and set up number formats. these objects also
    // parse numbers input by user
    private void setUpFormats() {
        moneyFormat = NumberFormat.getCurrencyInstance(Locale.US);
        //XXXX: Workaround. With an empty positive suffix
        //the format allows letters in the number.
        ((DecimalFormat)moneyFormat).setPositiveSuffix(" ");

        percentFormat = NumberFormat.getPercentInstance(Locale.US);
        percentFormat.setMinimumFractionDigits(3);
    }
}