Java Tutorial/Swing Event/MouseWheelListener

Handle mouse wheel event

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);
  }
}

How to Write a Mouse-Wheel Listener

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

/*
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 * Copyright (c) 1998 Sun Microsystems, Inc. All Rights Reserved.
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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);
  }
}

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

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);
  }
}