Java Tutorial/Swing Event/MouseWheelListener

Handle mouse wheel event

   <source lang="java">

import java.awt.event.MouseWheelEvent; import java.awt.event.MouseWheelListener; import javax.swing.JFrame; import javax.swing.JTextArea; public class Main extends JFrame {

 public Main() {
   setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
   setSize(200, 200);
   JTextArea textArea = new JTextArea();
   textArea.addMouseWheelListener(new MouseWheelListener() {
     public void mouseWheelMoved(MouseWheelEvent e) {
       if (e.getWheelRotation() < 0) {
         System.out.println("Up... " + e.getWheelRotation());
       } else {
         System.out.println("Down... " + e.getWheelRotation());
       }
       System.out.println("ScrollAmount: " + e.getScrollAmount());
       if (e.getScrollType() == MouseWheelEvent.WHEEL_UNIT_SCROLL) {
         System.out.println("MouseWheelEvent.WHEEL_UNIT_SCROLL");
       }
       if (e.getScrollType() == MouseWheelEvent.WHEEL_BLOCK_SCROLL) {
         System.out.println("MouseWheelEvent.WHEEL_BLOCK_SCROLL");
       }
     }
   });
   getContentPane().add(textArea);
 }
 public static void main(String[] args) {
   new Main().setVisible(true);
 }

}</source>

How to Write a Mouse-Wheel Listener

Mouse-wheel events tell you when the wheel on the mouse rotates.

   <source lang="java">

/*

*
* Copyright (c) 1998 Sun Microsystems, Inc. All Rights Reserved.
*
* Sun grants you ("Licensee") a non-exclusive, royalty free, license to use,
* modify and redistribute this software in source and binary code form,
* provided that i) this copyright notice and license appear on all copies of
* the software; and ii) Licensee does not utilize the software in a manner
* which is disparaging to Sun.
*
* This software is provided "AS IS," without a warranty of any kind. ALL
* EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING ANY
* IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR
* NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN AND ITS LICENSORS SHALL NOT BE
* LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING
* OR DISTRIBUTING THE SOFTWARE OR ITS DERIVATIVES. IN NO EVENT WILL SUN OR ITS
* LICENSORS BE LIABLE FOR ANY LOST REVENUE, PROFIT OR DATA, OR FOR DIRECT,
* INDIRECT, SPECIAL, CONSEQUENTIAL, INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER
* CAUSED AND REGARDLESS OF THE THEORY OF LIABILITY, ARISING OUT OF THE USE OF
* OR INABILITY TO USE SOFTWARE, EVEN IF SUN HAS BEEN ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGES.
*
* This software is not designed or intended for use in on-line control of
* aircraft, air traffic, aircraft navigation or aircraft communications; or in
* the design, construction, operation or maintenance of any nuclear
* facility. Licensee represents and warrants that it will not use or
* redistribute the Software for such purposes.
*/

import java.awt.BorderLayout; import java.awt.Dimension; import java.awt.event.MouseWheelEvent; import java.awt.event.MouseWheelListener; import javax.swing.BorderFactory; import javax.swing.JComponent; import javax.swing.JFrame; import javax.swing.JPanel; import javax.swing.JScrollPane; import javax.swing.JTextArea; public class MouseWheelEventDemo extends JPanel implements MouseWheelListener {

 JTextArea textArea = new JTextArea();
 JScrollPane scrollPane = new JScrollPane(textArea);
 final static String newline = "\n";
 public MouseWheelEventDemo() {
   super(new BorderLayout());
   textArea.setEditable(false);
   
   scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
   scrollPane.setPreferredSize(new Dimension(400, 250));
   add(scrollPane, BorderLayout.CENTER);
   textArea.append("This text area displays information " + "about its mouse wheel events."
       + newline);
   textArea.addMouseWheelListener(this);
   setPreferredSize(new Dimension(450, 350));
   setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
 }
 public void mouseWheelMoved(MouseWheelEvent e) {
   String message;
   int notches = e.getWheelRotation();
   if (notches < 0) {
     message = "Mouse wheel moved UP " + -notches + " notch(es)" + newline;
   } else {
     message = "Mouse wheel moved DOWN " + notches + " notch(es)" + newline;
   }
   if (e.getScrollType() == MouseWheelEvent.WHEEL_UNIT_SCROLL) {
     message += "    Scroll type: WHEEL_UNIT_SCROLL" + newline;
     message += "    Scroll amount: " + e.getScrollAmount() + " unit increments per notch"
         + newline;
     message += "    Units to scroll: " + e.getUnitsToScroll() + " unit increments" + newline;
     message += "    Vertical unit increment: "
         + scrollPane.getVerticalScrollBar().getUnitIncrement(1) + " pixels" + newline;
   } else { // scroll type == MouseWheelEvent.WHEEL_BLOCK_SCROLL
     message += "    Scroll type: WHEEL_BLOCK_SCROLL" + newline;
     message += "    Vertical block increment: "
         + scrollPane.getVerticalScrollBar().getBlockIncrement(1) + " pixels" + newline;
   }
   saySomething(message, e);
 }
 void saySomething(String eventDescription, MouseWheelEvent e) {
   textArea.append(e.getComponent().getClass().getName() + ": " + eventDescription);
   textArea.setCaretPosition(textArea.getDocument().getLength());
 }
 public static void main(String[] args) {
   JFrame frame = new JFrame("MouseWheelEventDemo");
   frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
   JComponent newContentPane = new MouseWheelEventDemo();
   newContentPane.setOpaque(true); // content panes must be opaque
   frame.setContentPane(newContentPane);
   frame.pack();
   frame.setVisible(true);
 }

}</source>

The MouseWheelListener Interface: defines a method to respond to the mouse wheel being rotated

Defined MethodDescriptionmouseWheelMoved(MouseWheelEvent e)Called when the mouse wheel is rotated

   <source lang="java">

import java.awt.Graphics; import java.awt.event.MouseWheelEvent; import java.awt.event.MouseWheelListener; import java.awt.image.BufferedImage; import java.io.File; import javax.imageio.ImageIO; import javax.swing.JFrame; public class ZoomingViewer extends JFrame {

 private BufferedImage bi;
 private int zoom = 0;
 private static final double ZOOM_AMOUNT = 1.1;
 public static void main(String[] args) {
     new ZoomingViewer("your.jpg").setVisible(true);
 }
 private void sizeToZoom() {
   double factor = Math.pow(ZOOM_AMOUNT, zoom);
   setSize((int) (bi.getWidth() * factor), (int) (bi.getHeight() * factor));
 }
 public ZoomingViewer(String filename) {
   setDefaultCloseOperation(EXIT_ON_CLOSE);
   try {
     bi = ImageIO.read(new File(filename));
   } catch (Exception e) {
     e.printStackTrace();
   }
   sizeToZoom();
   addMouseWheelListener(new MouseWheelListener() {
     public void mouseWheelMoved(MouseWheelEvent e) {
       int steps = e.getWheelRotation();
       zoom += steps;
       sizeToZoom();
     }
   });
 }
 public void paint(Graphics g) {
   g.drawImage(bi, 0, 0, getWidth(), getHeight(), this);
 }

}</source>