formattedtextfielddemo.java

这是一个英文版的《Java程序设计与问题解决》现在好多大学都当成教材

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

import javax.swing.*;
import javax.swing.event.*;
import javax.swing.text.*;

import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeEvent;

import java.text.*;

/**
 * Implements a panel containing mortgage-calculating fields, suitable
 * for use as a content pane.  For standalone use, the main method
 * creates a JFrame and puts the panel inside it.
 */
public class FormattedTextFieldDemo extends JPanel
                                    implements PropertyChangeListener {
    //Values for the text fields
    private double amount = 100000;
    private double rate = 7.5;  //7.5 %
    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 JFormattedTextField amountField;
    private JFormattedTextField rateField;
    private JFormattedTextField numPeriodsField;
    private JFormattedTextField paymentField;

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

    public FormattedTextFieldDemo() {
        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.
        amountField = new JFormattedTextField(moneyFormat);
        amountField.setValue(new Double(amount));
        amountField.setColumns(10);
        amountField.addPropertyChangeListener(this);
        amountField.setFocusLostBehavior(
            JFormattedTextField.COMMIT_OR_REVERT);

        rateField = new JFormattedTextField(percentFormat);
        rateField.setValue(new Double(rate));
        rateField.setColumns(10);
        rateField.addPropertyChangeListener(this);
        rateField.setFocusLostBehavior(
            JFormattedTextField.COMMIT_OR_REVERT);
        numPeriodsField = new JFormattedTextField();
        numPeriodsField.setValue(new Integer(numPeriods));
        numPeriodsField.setColumns(10);
        numPeriodsField.addPropertyChangeListener(this);
        numPeriodsField.setFocusLostBehavior(
            JFormattedTextField.COMMIT_OR_REVERT);

        paymentField = new JFormattedTextField(paymentFormat);
        paymentField.setValue(new Double(payment));
        paymentField.setColumns(10);
        paymentField.setEditable(false);
        paymentField.setForeground(Color.red);

        //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();
        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 this panel, labels on left,
        //text fields on right.
        setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
        setLayout(new BorderLayout());
        add(labelPane, BorderLayout.CENTER);
        add(fieldPane, BorderLayout.LINE_END);
    }

    public void propertyChange(PropertyChangeEvent e) {
        if ("value".equals(e.getPropertyName())) {
            Object source = e.getSource();
            if (source == amountField) {
                amount = ((Number)amountField.getValue()).doubleValue();
            } else if (source == rateField) {
                rate = ((Number)rateField.getValue()).doubleValue();
            } else if (source == numPeriodsField) {
                numPeriods = ((Number)numPeriodsField.getValue()).intValue();
            }

            payment = computePayment(amount, rate, numPeriods);
            paymentField.setValue(new Double(payment));
        }
    }

    public static void main(String[] args) {
        //Make sure we have nice window decorations.
        JFrame.setDefaultLookAndFeelDecorated(true);

        //Create and set up the window.
        JFrame frame = new JFrame("FormattedTextFieldDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setContentPane(new FormattedTextFieldDemo());

        //Display the window.
        frame.pack();
        frame.setVisible(true);
    }

    //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;

        I = rate / 100.0 / 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.getNumberInstance();

        percentFormat = NumberFormat.getNumberInstance();
        percentFormat.setMinimumFractionDigits(3);

        paymentFormat = (DecimalFormat)NumberFormat.getNumberInstance();
        paymentFormat.setMaximumFractionDigits(2);
        paymentFormat.setNegativePrefix("(");
        paymentFormat.setNegativeSuffix(")");
    }
}