CelsiusConverter.java

/**
 * A simple Swing UI demonstrating the use of JButton, JTextField and JLabel.
 * Code contributed by Satadip Dutta was labeled <code>v 1.3</code>, and was
 * extended/revised by Tom Roche & Tim Wall.
 *   
 * @author Satadip Dutta
 * @version $Id: CelsiusConverter.java,v 1.1 2006-11-03 18:52:42 pq Exp $
 */

package example;

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import java.text.DecimalFormat;
import java.text.MessageFormat;

import javax.swing.BorderFactory;
import javax.swing.ButtonGroup;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JPanel;
import javax.swing.JRadioButtonMenuItem;
import javax.swing.JTextField;
import javax.swing.SwingConstants;
import javax.swing.UIManager;

public class CelsiusConverter extends JPanel {
    private static final int NPRECISIONS = 5;
    private int precision;
    private JLabel celsiusLabel;
    private JLabel fahrLabel;
    private JTextField inputText;

    // Constructor
    public CelsiusConverter() {
        // Create the container.
        final int MARGIN = 2;
        setLayout(new GridLayout(0, 2, MARGIN, MARGIN));
        setBorder(BorderFactory.createEmptyBorder(MARGIN, MARGIN, MARGIN, MARGIN));

        JPanel left = new JPanel(new BorderLayout());
        left.setBorder(BorderFactory.createEtchedBorder());
        add(left);

        JPanel right = new JPanel(new BorderLayout());
        right.setBorder(BorderFactory.createEtchedBorder());
        add(right);

        // Create widgets.
        inputText = new JTextField(2);
        final JButton convertTemp = new JButton(lookupString("conversion.button.text")); //$NON-NLS-1$
        celsiusLabel = new JLabel(lookupString("input.label.text"), SwingConstants.LEFT); //$NON-NLS-1$
        fahrLabel = new JLabel(lookupString("output.label.text"), SwingConstants.LEFT); //$NON-NLS-1$

        // Add widgets to container.
        left.add(inputText, BorderLayout.NORTH);
        left.add(convertTemp, BorderLayout.SOUTH);

        right.add(celsiusLabel, BorderLayout.NORTH);
        right.add(fahrLabel, BorderLayout.SOUTH);

        celsiusLabel.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));
        fahrLabel.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));

        // Listen to events from Convert button.
        convertTemp.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent event) {
                    updateLabels();
                }
            });
        inputText.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    convertTemp.doClick();
                }
            });
    }

    /** Convert the given Celsius value to Fahrenheit. */
    public static double convert(double celsius) {
        return celsius * 9 / 5 + 32;
    }

    // convenience
    public static String lookupString(String key) {
        return CelsiusConverterStrings.getString(key);
    }
	
    // convenience, reused in tests
    public static String formatOutput(String format, double value,
                                      int precision) {
        MessageFormat f = new MessageFormat(format);
        String pattern = "#";
        if (precision > 0)
            pattern += ".";
        while (precision-- > 0)
            pattern += "#";
        DecimalFormat dfmt = new DecimalFormat(pattern);
        return f.format(new Object[] { dfmt.format(value) });
    }

    // convenience, reused in tests
    public static String fahrenheitOutput(double value, int precision) {
        return formatOutput(lookupString("F"), value, precision);
    }

    // convenience, reused in tests
    public static String celsiusOutput(double value, int precision) {
        return formatOutput(lookupString("C"), value, precision);
    }

    private void updateLabels() {
        String in = inputText.getText();
        try {
            // Convert degrees Celsius to Fahrenheit.
            double celsius = Double.parseDouble(in);
            celsiusLabel.setText(formatOutput(lookupString("C"),
                                              celsius,
                                              precision)); //$NON-NLS-1$
            double fahr = convert(celsius);
            fahrLabel.setText(formatOutput(lookupString("F"), fahr,
                                           precision)); //$NON-NLS-1$
        } catch (Exception e){
            inputText.selectAll();
        }
    }

    private JMenuBar createMenuBar() {

        JMenuBar menuBar = new JMenuBar();
        JMenu menu = new JMenu(lookupString("menu.options"));
        menuBar.add(menu);
        JMenu submenu = new JMenu(lookupString("menu.precision"));
        menu.add(submenu);
        ActionListener listener = new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    if (((JRadioButtonMenuItem)e.getSource()).isSelected()) {
                        precision = Integer.parseInt(e.getActionCommand());
                        updateLabels();
                    }
                }
            };
        ButtonGroup group = new ButtonGroup();
        for (int i=0;i < NPRECISIONS;i++) {
            JRadioButtonMenuItem item =
                new JRadioButtonMenuItem(String.valueOf(i), i==precision);
            item.setActionCommand(String.valueOf(i));
            item.addActionListener(listener);
            group.add(item);
            submenu.add(item);
        }

        return menuBar;
    }

    /**
     * Stick us in a <code>JFrame</code>.
     * Reused in tests.
     */
    public void enframe(JFrame frame) {
        frame.setTitle(lookupString("frame.title")); //$NON-NLS-1$
        // Add the panel to the frame.
        frame.setContentPane(this);
        frame.setJMenuBar(createMenuBar());

        // Exit when the window is closed.
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        frame.pack();
        Dimension d = frame.getSize();
        d.width = Math.max(d.width, 350);
        frame.setSize(d);
    }

    // main method
    public static void main(String[] args) {
        try {
            UIManager.setLookAndFeel(UIManager.getCrossPlatformLookAndFeelClassName());
        }
        catch (Exception e) {
            e.printStackTrace();
            System.exit(1);
        }
        CelsiusConverter converter = new CelsiusConverter();
        JFrame frame = new JFrame();
        converter.enframe(frame);
        frame.setVisible(true);
    }

}