DoubleClickDetector

package doubleclick;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.plaf.basic.*;

/** A window to demo double-clicking.  Single clicks will increment the
 * number in the JLabel.  Double clicks will cause the number to become
 * zero if it is eight or larger.  Hence, while the number is six or
 * less a double-click will do nothing and the second click will act
 * as a second single click.  A double-click when the number is seven
 * will set it to zero:  the first click bumps it up to eight and the
 * double-click code sees it as eight and zeroes it. */
public class DoubleClickExample  extends JFrame  {

    /** Creates and makes visible a window. */
    public static void main( String[] args )  {
        new DoubleClickExample().setVisible( true );
    }

    /** Mouse listener that increments a number. */
    private MouseListener  inc = new MouseAdapter()  {
        public void mousePressed( MouseEvent me )  {
            if (me.isConsumed())
                // Someone else already used this click.  Do nothing.
                return;
            number += 1;
            nLabel.setText( Integer.toString( number ) );
            me.consume();
        }
    };

    /** Double-click listener that turns a number greater than 8
     * into a zero. */
    private DoubleClickDetector.Listener
                dcdListen = new DoubleClickDetector.Listener()  {
        public boolean doubleClick( MouseEvent me )  {
            if (number < 8)
                // Double-click did nothing.  Allow next mouse listener
                // to see second click as a simple "Mouse Pressed" event.
                // (Set return to "true" to be seriously annoying.)
                return false;
            number = 0;
            nLabel.setText( "0" );
            // Double-click did something.  Prevent next mouse listener
            // from reacting to second click.
            return true;
        }
    };

    private int     number = 0;
    private JLabel  nLabel = new JLabel( "0" );

    /** Creates a new DoubleClickExampleWindow. */
    public DoubleClickExample()  {
        setBounds( 100, 100, 280, 160 );
        setDefaultCloseOperation( EXIT_ON_CLOSE );
        Container  cp = getContentPane();
        cp.setLayout( null );

        nLabel.setBounds( 80, 50, 120, 24 );
        nLabel.setBackground( Color.WHITE );
        nLabel.setOpaque( true );
        nLabel.setBorder( BasicBorders.getTextFieldBorder() );
        nLabel.setHorizontalAlignment( JLabel.CENTER );
        add( nLabel );

        // Adds a double-click listener so it can intercept,
        // if it should, other mouse listeners.
        cp.addMouseListener( new DoubleClickDetector( dcdListen ) );

        // Add mouse listener to increment number.
        cp.addMouseListener( inc );
    }
}

Javadoc for DoubleClickDetector in plain text:

doubleclick Class DoubleClickDetector

java.lang.Object doubleclick.DoubleClickDetector

All Implemented Interfaces: java.awt.event.MouseListener, java.util.EventListener

public class DoubleClickDetector extends java.lang.Object implements java.awt.event.MouseListener

A handy MouseListener implementation that detects double-clicks. This detector will pick up the second click even if the mouse moves a bit (up to 10 pixels) between clicks, so beginning mouseketteers will not be so much fun to watch, but otherwise it works very well. The second click is consumed, to keep it from causing other problems.

To use, create a DoubleClickDetector and add a DoubleClickDetector.Listener to it. Then add it as a MouseListener to a java.awt.Component. Note that mouse listeners are invoked in the order in which they are added to a component. If a previously added listener consumes a Mouse Pressed MouseEvent before this listener gets it, this listener will ignore it as the second (but not first) click in a double-click. (Other consumed mouse events are not ignored; once a Mouse Pressed event comes through, consumed or unconsumed, DoubleClickDetector is irrevocably committed to detecting a double-click.)

Java Windows note: if a Component has a mouse listener added to it, its parent will not receive mouse click events from its location. Double-click philosophical note: a double click is supposed to do a second action after the action of the first click. It should always do the same thing as a single click. It should not do a single click twice unless the double-click is unable to do its second action. In that case a double-click should work just like two single-clicks.

Mouse events happen only on the Event Queue. Adding, removing, and getting listeners may be done on any thread at any time; the class is thread-safe.

Nested Class Summary

static interface DoubleClickDetector.Listener The listener interface for detecting double clicks.

Constructor Detail

DoubleClickDetector()

public DoubleClickDetector()

Creates a new DoubleClickDetector.

DoubleClickDetector()

public DoubleClickDetector(DoubleClickDetector.Listener l)

Creates a new DoubleClickDetector and adds a Listener to it. (Turns a two-step process into a one-step process.)

Parameters:

• l - a listener.

Method Detail

addListener()

public void addListener(DoubleClickDetector.Listener l)

Adds a listener for double-clicks. These will be checked in the order added. (If the first listener does not use the double-click, the second will be notified. If the second does use it, no more listeners will be called and all mouse events relating to the double-click will be marked as consumed. The use of more than one listener will be rare.)

removeListener()

public void removeListener(DoubleClickDetector.Listenerl)

Removes a listener for double-clicks.

getListeners()

public DoubleClickDetector.Listener[] getListeners()

Returns an independent array of listeners, in order. Never returns null, but may return an empty array (an array of length zero).

Javadoc for DoubleClickDetector.Listener in plain text:

doubleclick Interface DoubleClickDetector.Listener

Enclosing class: DoubleClickDetector

public static interface DoubleClickDetector.Listener

The listener interface for detecting double clicks.

Method Detail

doubleClick()

boolean doubleClick(java.awt.event.MouseEvent e)

Called when a valid double click is detected.

Parameters: * 'e' - the event for the first mouse click. Will be a Mouse Released event.

Returns: true if the double click was accepted, false if it was not used. If true, the (second) click will be consumed. If false, this click will not be consumed, and hopefully will register as an independent, valid click in its own right in some other MouseListener. (Conceivably, the discarded second click could end up as the second click in a second DoubleClickDetector object.)