Java example source code file (CheckboxMenuItem.java)

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Java - Java tags/keywords

accessibleaction, accessibleawtcheckboxmenuitem, accessibleawtmenuitem, accessiblevalue, awt, checkboxmenuitem, event, eventlistener, headlessexception, itemevent, itemlistener, number, object, string, util

The CheckboxMenuItem.java Java example source code

/*
 * Copyright (c) 1995, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */
package java.awt;

import java.awt.peer.CheckboxMenuItemPeer;
import java.awt.event.*;
import java.util.EventListener;
import java.io.ObjectOutputStream;
import java.io.ObjectInputStream;
import java.io.IOException;
import javax.accessibility.*;
import sun.awt.AWTAccessor;


/**
 * This class represents a check box that can be included in a menu.
 * Selecting 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:
 * <p>
 * <img src="doc-files/MenuBar-1.gif"
 * alt="Menu labeled Examples, containing items Basic, Simple, Check, and More Examples. The Check item is a CheckBoxMenuItem instance, in the off state."
 * style="float:center; margin: 7px 10px;">
 * <p>
 * The item labeled <code>Check 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,
 * the <code>processEvent method examines the event and passes
 * it along to <code>processItemEvent. The latter method redirects
 * the event to any <code>ItemListener objects that have
 * registered an interest in item events generated by this menu item.
 *
 * @author      Sami Shaio
 * @see         java.awt.event.ItemEvent
 * @see         java.awt.event.ItemListener
 * @since       JDK1.0
 */
public class CheckboxMenuItem extends MenuItem implements ItemSelectable, Accessible {

    static {
        /* ensure that the necessary native libraries are loaded */
        Toolkit.loadLibraries();
        if (!GraphicsEnvironment.isHeadless()) {
            initIDs();
        }

        AWTAccessor.setCheckboxMenuItemAccessor(
            new AWTAccessor.CheckboxMenuItemAccessor() {
                public boolean getState(CheckboxMenuItem cmi) {
                    return cmi.state;
                }
            });
    }

   /**
    * The state of a checkbox menu item
    * @serial
    * @see #getState()
    * @see #setState(boolean)
    */
    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."
     * @exception HeadlessException if GraphicsEnvironment.isHeadless()
     * returns true
     * @see java.awt.GraphicsEnvironment#isHeadless
     * @since   JDK1.1
     */
    public CheckboxMenuItem() throws HeadlessException {
        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 for an unlabeled menu item.
     * @exception HeadlessException if GraphicsEnvironment.isHeadless()
     * returns true
     * @see java.awt.GraphicsEnvironment#isHeadless
     */
    public CheckboxMenuItem(String label) throws HeadlessException {
        this(label, false);
    }

    /**
     * Create a check box menu item with the specified label and state.
     * @param      label   a string label for the check box menu item,
     *                     or <code>null for an unlabeled menu item.
     * @param      state   the initial state of the menu item, where
     *                     <code>true indicates "on" and
     *                     <code>false indicates "off."
     * @exception HeadlessException if GraphicsEnvironment.isHeadless()
     * returns true
     * @see java.awt.GraphicsEnvironment#isHeadless
     * @since      JDK1.1
     */
    public CheckboxMenuItem(String label, boolean state)
        throws HeadlessException {
        super(label);
        this.state = state;
    }

    /**
     * Construct a name for this MenuComponent.  Called by getName() when
     * the name is null.
     */
    String constructComponentName() {
        synchronized (CheckboxMenuItem.class) {
            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()
     */
    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 indicates "on" and
     *                     <code>false indicates "off"
     * @see        #setState
     */
    public boolean getState() {
        return state;
    }

    /**
     * Sets this check box menu item to the specified state.
     * The boolean value <code>true indicates "on" while
     * <code>false indicates "off."
     *
     * <p>Note that this method should be primarily used to
     * initialize the state of the check box menu item.
     * Programmatically setting the state of the check box
     * menu item will <i>not trigger
     * an <code>ItemEvent.  The only way to trigger an
     * <code>ItemEvent is by user interaction.
     *
     * @param      b   <code>true if the check box
     *             menu item is on, otherwise <code>false
     * @see        #getState
     */
    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.  Item events are sent in response to user
     * actions, but not in response to calls to setState().
     * If l is null, no exception is thrown and no action is performed.
     * <p>Refer to  for details on AWT's threading model.
     *
     * @param         l the item listener
     * @see           #removeItemListener
     * @see           #getItemListeners
     * @see           #setState
     * @see           java.awt.event.ItemEvent
     * @see           java.awt.event.ItemListener
     * @since         JDK1.1
     */
    public synchronized void addItemListener(ItemListener l) {
        if (l == null) {
            return;
        }
        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.
     * If l is null, no exception is thrown and no action is performed.
     * <p>Refer to  for details on AWT's threading model.
     *
     * @param         l the item listener
     * @see           #addItemListener
     * @see           #getItemListeners
     * @see           java.awt.event.ItemEvent
     * @see           java.awt.event.ItemListener
     * @since         JDK1.1
     */
    public synchronized void removeItemListener(ItemListener l) {
        if (l == null) {
            return;
        }
        itemListener = AWTEventMulticaster.remove(itemListener, l);
    }

    /**
     * Returns an array of all the item listeners
     * registered on this checkbox menuitem.
     *
     * @return all of this checkbox menuitem's <code>ItemListeners
     *         or an empty array if no item
     *         listeners are currently registered
     *
     * @see           #addItemListener
     * @see           #removeItemListener
     * @see           java.awt.event.ItemEvent
     * @see           java.awt.event.ItemListener
     * @since 1.4
     */
    public synchronized ItemListener[] getItemListeners() {
        return getListeners(ItemListener.class);
    }

    /**
     * Returns an array of all the objects currently registered
     * as <code>FooListeners
     * upon this <code>CheckboxMenuItem.
     * <code>FooListeners are registered using the
     * <code>addFooListener method.
     *
     * <p>
     * You can specify the <code>listenerType argument
     * with a class literal, such as
     * <code>FooListener.class.
     * For example, you can query a
     * <code>CheckboxMenuItem c
     * for its item listeners with the following code:
     *
     * <pre>ItemListener[] ils = (ItemListener[])(c.getListeners(ItemListener.class));