checkboxmenuitem.java

《移动Agent技术》一书的所有章节源代码。

/*
 * @(#)CheckboxMenuItem.java	1.31 98/08/21
 *
 * Copyright 1995-1998 by Sun Microsystems, Inc.,
 * 901 San Antonio Road, Palo Alto, California, 94303, U.S.A.
 * All rights reserved.
 *
 * This software is the confidential and proprietary information
 * of Sun Microsystems, Inc. ("Confidential Information").  You
 * shall not disclose such Confidential Information and shall use
 * it only in accordance with the terms of the license agreement
 * you entered into with Sun.
 */
package java.awt;

import java.awt.peer.CheckboxMenuItemPeer;
import java.awt.event.*;
import java.io.ObjectOutputStream;
import java.io.ObjectInputStream;
import java.io.IOException;


/**
 * This class represents a check box that can be included in a menu.
 * Clicking on the check box in the menu changes its state from
 * "on" to "off" or from "off" to "on."
 * <p>
 * The following picture depicts a menu which contains an instance
 * of <code>CheckBoxMenuItem</code>:
 * <p>
 * <img src="images-awt/MenuBar-1.gif"
 * ALIGN=center HSPACE=10 VSPACE=7>
 * <p>
 * The item labeled <code>Check</code> shows a check box menu item
 * in its "off" state.
 * <p>
 * When a check box menu item is selected, AWT sends an item event to
 * the item. Since the event is an instance of <code>ItemEvent</code>,
 * the <code>processEvent</code> method examines the event and passes
 * it along to <code>processItemEvent</code>. The latter method redirects
 * the event to any <code>ItemListener</code> objects that have
 * registered an interest in item events generated by this menu item.
 *
 * @version 1.31, 08/21/98
 * @author 	Sami Shaio
 * @see         java.awt.event.ItemEvent
 * @see         java.awt.event.ItemListener
 * @since       JDK1.0
 */
public class CheckboxMenuItem extends MenuItem implements ItemSelectable {

    boolean state = false;

    transient ItemListener itemListener;

    private static final String base = "chkmenuitem";
    private static int nameCounter = 0;

    /*
     * JDK 1.1 serialVersionUID
     */
     private static final long serialVersionUID = 6190621106981774043L;

    /**
     * Create a check box menu item with an empty label.
     * The item's state is initially set to "off."
     * @since   JDK1.1
     */
    public CheckboxMenuItem() {
	this("", false);
    }

    /**
     * Create a check box menu item with the specified label.
     * The item's state is initially set to "off."

     * @param     label   a string label for the check box menu item,
     *                or <code>null</code> for an unlabeled menu item.
     * @since     JDK1.0
     */
    public CheckboxMenuItem(String label) {
	this(label, false);
    }

    /**
     * Create a check box menu item with the specified label and state.
     * @param      label   the button label.
     * @param      state   the initial state of the menu item, where
     *                     <code>true</code> indicates "on" and
     *                     <code>false</code> indicates "off."
     * @since      JDK1.1
     */
    public CheckboxMenuItem(String label, boolean state) {
        super(label);
    	this.state = state;
    }

    /**
     * Construct a name for this MenuComponent.  Called by getName() when
     * the name is null.
     */
    String constructComponentName() {
	return base + nameCounter++;
    }

    /**
     * Creates the peer of the checkbox item.  This peer allows us to
     * change the look of the checkbox item without changing its
     * functionality.
     * Most applications do not call this method directly.
     * @see     java.awt.Toolkit#createCheckboxMenuItem(java.awt.CheckboxMenuItem)
     * @see     java.awt.Component#getToolkit()
     * @since   JDK1.0
     */
    public void addNotify() {
        synchronized (getTreeLock()) {
	    if (peer == null)
			peer = Toolkit.getDefaultToolkit().createCheckboxMenuItem(this);
	    super.addNotify();
        }
    }

    /**
     * Determines whether the state of this check box menu item
     * is "on" or "off."
     * @return      the state of this check box menu item, where
     *                     <code>true</code> indicates "on" and
     *                     <code>false</code> indicates "off."
     * @see        java.awt.CheckboxMenuItem#setState
     * @since      JDK1.0
     */
    public boolean getState() {
	return state;
    }

    /**
     * Sets this check box menu item to the specifed state.
     * The boolean value <code>true</code> indicates "on" while
     * <code>false</code> indicates "off."
     * @param      b   the boolean state of this
     *                      check box menu item.
     * @see        java.awt.CheckboxMenuItem#getState
     * @since      JDK1.0
     */
    public synchronized void setState(boolean b) {
	state = b;
	CheckboxMenuItemPeer peer = (CheckboxMenuItemPeer)this.peer;
	if (peer != null) {
	    peer.setState(b);
	}
    }

    /**
     * Returns the an array (length 1) containing the checkbox menu item
     * label or null if the checkbox is not selected.
     * @see ItemSelectable
     */
    public synchronized Object[] getSelectedObjects() {
        if (state) {
            Object[] items = new Object[1];
            items[0] = label;
            return items;
        }
        return null;
    }

    /**
     * Adds the specified item listener to receive item events from
     * this check box menu item.
     * @param         l the item listener.
     * @see           java.awt.event.ItemEvent
     * @see           java.awt.event.ItemListener
     * @see           java.awt.Choice#removeItemListener
     * @since         JDK1.1
     */
    public synchronized void addItemListener(ItemListener l) {
        itemListener = AWTEventMulticaster.add(itemListener, l);
        newEventsOnly = true;
    }

    /**
     * Removes the specified item listener so that it no longer receives
     * item events from this check box menu item.
     * @param         l the item listener.
     * @see           java.awt.event.ItemEvent
     * @see           java.awt.event.ItemListener
     * @see           java.awt.Choice#addItemListener
     * @since         JDK1.1
     */
    public synchronized void removeItemListener(ItemListener l) {
        itemListener = AWTEventMulticaster.remove(itemListener, l);
    }

    // REMIND: remove when filtering is done at lower level
    boolean eventEnabled(AWTEvent e) {
        if (e.id == ItemEvent.ITEM_STATE_CHANGED) {
            if ((eventMask & AWTEvent.ITEM_EVENT_MASK) != 0 ||
                itemListener != null) {
                return true;
            }
            return false;
        }
        return super.eventEnabled(e);
    }

    /**
     * Processes events on this check box menu item.
     * If the event is an instance of <code>ItemEvent</code>,
     * this method invokes the <code>processItemEvent</code> method.
     * If the event is not an item event,
     * it invokes <code>processEvent</code> on the superclass.
     * <p>
     * Check box menu items currently support only item events.
     * @param        e the event
     * @see          java.awt.event.ItemEvent
     * @see          java.awt.CheckboxMenuItem#processItemEvent
     * @since        JDK1.1
     */
    protected void processEvent(AWTEvent e) {
        if (e instanceof ItemEvent) {
            processItemEvent((ItemEvent)e);
	    return;
        }
	super.processEvent(e);
    }

    /**
     * Processes item events occurring on this check box menu item by
     * dispatching them to any registered <code>ItemListener</code> objects.
     * <p>
     * This method is not called unless item events are
     * enabled for this menu item. Item events are enabled
     * when one of the following occurs:
     * <p><ul>
     * <li>An <code>ItemListener</code> object is registered
     * via <code>addItemListener</code>.
     * <li>Item events are enabled via <code>enableEvents</code>.
     * </ul>
     * @param       e the item event.
     * @see         java.awt.event.ItemEvent
     * @see         java.awt.event.ItemListener
     * @see         java.awt.CheckboxMenuItem#addItemListener
     * @see         java.awt.MenuItem#enableEvents
     * @since       JDK1.1
     */
    protected void processItemEvent(ItemEvent e) {
        if (itemListener != null) {
            itemListener.itemStateChanged(e);
        }
    }

    /**
     * Returns the parameter string representing the state of this check
     * box menu item. This string is useful for debugging.
     * @return     the parameter string of this check box menu item.
     * @since      JDK1.0
     */
    public String paramString() {
	return super.paramString() + ",state=" + state;
    }

    /* Serialization support.
     */

    private int checkboxMenuItemSerializedDataVersion = 1;


    private void writeObject(ObjectOutputStream s)
      throws java.io.IOException
    {
      s.defaultWriteObject();

      AWTEventMulticaster.save(s, itemListenerK, itemListener);
      s.writeObject(null);
    }


    private void readObject(ObjectInputStream s)
      throws ClassNotFoundException, IOException
    {
      s.defaultReadObject();

      Object keyOrNull;
      while(null != (keyOrNull = s.readObject())) {
	String key = ((String)keyOrNull).intern();

	if (itemListenerK == key)
	  addItemListener((ItemListener)(s.readObject()));

	else // skip value for unrecognized key
	  s.readObject();
      }
    }
}