DigitalClock.java Source code

Introduction

Here is the source code for DigitalClock.java

Source

/*
 * Copyright (c) 2004 David Flanagan.  All rights reserved.
 * This code is from the book Java Examples in a Nutshell, 3nd Edition.
 * It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.
 * You may study, use, and modify it for any non-commercial purpose,
 * including teaching and use in open-source projects.
 * You may distribute it non-commercially as long as you retain this notice.
 * For a commercial use license, or to purchase the book, 
 * please visit http://www.davidflanagan.com/javaexamples3.
 */

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;
import java.awt.event.InputEvent;
import java.awt.event.KeyEvent;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
import java.text.DateFormat;
import java.util.Date;

import javax.swing.ActionMap;
import javax.swing.InputMap;
import javax.swing.JLabel;
import javax.swing.KeyStroke;
import javax.swing.Timer;
import javax.swing.TransferHandler;
import javax.swing.border.LineBorder;

/**
 * A custom Swing component that displays a simple digital clock. Demonstrates
 * how to add copy and drag support to a Swing component with TransferHandler.
 */
public class DigitalClock extends JLabel {
    DateFormat format; // How to display the time in string form

    int updateFrequency; // How often to update the time (in milliseconds)

    Timer timer; // Triggers repeated updates to the clock

    public DigitalClock() {
        // Set default values for our properties
        setFormat(DateFormat.getTimeInstance(DateFormat.MEDIUM, getLocale()));
        setUpdateFrequency(1000); // Update once a second

        // Specify a Swing TransferHandler object to do the dirty work of
        // copy-and-paste and drag-and-drop for us. This one will transfer
        // the value of the "time" property. Since this property is read-only
        // it will allow drags but not drops.
        setTransferHandler(new TransferHandler("time"));

        // Since JLabel does not normally support drag-and-drop, we need an
        // event handler to detect a drag and start the transfer.
        addMouseMotionListener(new MouseMotionAdapter() {
            public void mouseDragged(MouseEvent e) {
                getTransferHandler().exportAsDrag(DigitalClock.this, e, TransferHandler.COPY);
            }
        });

        // Before we can have a keyboard binding for a Copy command,
        // the component needs to be able to accept keyboard focus.
        setFocusable(true);
        // Request focus when we're clicked on
        addMouseListener(new MouseAdapter() {
            public void mouseClicked(MouseEvent e) {
                requestFocus();
            }
        });
        // Use a LineBorder to indicate when we've got the keyboard focus
        addFocusListener(new FocusListener() {
            public void focusGained(FocusEvent e) {
                setBorder(LineBorder.createBlackLineBorder());
            }

            public void focusLost(FocusEvent e) {
                setBorder(null);
            }
        });

        // Now bind the Ctrl-C keystroke to a "Copy" command.
        InputMap im = new InputMap();
        im.setParent(getInputMap(WHEN_FOCUSED));
        im.put(KeyStroke.getKeyStroke(KeyEvent.VK_C, InputEvent.CTRL_MASK), "Copy");
        setInputMap(WHEN_FOCUSED, im);

        // And bind the "Copy" command to a pre-defined Action that performs
        // a copy using the TransferHandler we've installed.
        ActionMap am = new ActionMap();
        am.setParent(getActionMap());
        am.put("Copy", TransferHandler.getCopyAction());
        setActionMap(am);

        // Create a javax.swing.Timer object that will generate ActionEvents
        // to tell us when to update the displayed time. Every updateFrequency
        // milliseconds, this timer will cause the actionPerformed() method
        // to be invoked. (For non-GUI applications, see java.util.Timer.)
        timer = new Timer(updateFrequency, new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                setText(getTime()); // set label to current time string
            }
        });
        timer.setInitialDelay(0); // Do the first update immediately
        timer.start(); // Start timing now!
    }

    // Return the current time as a String.
    // This is the property accessor method used by the TransferHandler.
    // Since there is a getter, but no setter, the TransferHandler will
    // reject any attempts to drop data on us.
    public String getTime() {
        // Use the DateFormat object to convert current time to a string
        return format.format(new Date());
    }

    // Here are two related property setter methods
    public void setFormat(DateFormat format) {
        this.format = format;
    }

    public void setUpdateFrequency(int ms) {
        this.updateFrequency = ms;
    }
}