java/awt/CheckboxMenuItem.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is free software; you can redistribute it and/or modify it
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 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
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 * accompanied this code).
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package java.awt;

import java.awt.event.ActionListener;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.awt.peer.CheckboxMenuItemPeer;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.EventListener;

import javax.accessibility.Accessible;
import javax.accessibility.AccessibleAction;
import javax.accessibility.AccessibleContext;
import javax.accessibility.AccessibleRole;
import javax.accessibility.AccessibleValue;

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="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       1.0
 */
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)
    */
    private volatile boolean state;

    private transient volatile 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   1.1
     */
    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      1.1
     */
    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.Component#getToolkit()
     */
    public void addNotify() {
        synchronized (getTreeLock()) {
            if (peer == null)
                peer = getComponentFactory().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</i> 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 <a href="doc-files/AWTThreadIssues.html#ListenersThreads"
     * >AWT Threading Issues</a> 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         1.1
     */
    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 <a href="doc-files/AWTThreadIssues.html#ListenersThreads"
     * >AWT Threading Issues</a> 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         1.1
     */
    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 ItemListener}s
     *         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><em>Foo</em>Listener</code>s
     * upon this {@code CheckboxMenuItem}.
     * <code><em>Foo</em>Listener</code>s are registered using the
     * <code>add<em>Foo</em>Listener</code> method.
     *
     * <p>
     * You can specify the {@code listenerType} argument
     * with a class literal, such as
     * <code><em>Foo</em>Listener.class</code>.
     * 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));</pre>
     *
     * If no such listeners exist, this method returns an empty array.
     *
     * @param listenerType the type of listeners requested; this parameter
     *          should specify an interface that descends from
     *          {@code java.util.EventListener}
     * @return an array of all objects registered as
     *          <code><em>Foo</em>Listener</code>s on this checkbox menuitem,
     *          or an empty array if no such
     *          listeners have been added
     * @exception ClassCastException if {@code listenerType}
     *          doesn't specify a class or interface that implements
     *          {@code java.util.EventListener}
     *
     * @see #getItemListeners
     * @since 1.3
     */
    public <T extends EventListener> T[] getListeners(Class<T> listenerType) {
        EventListener l = null;
        if  (listenerType == ItemListener.class) {
            l = itemListener;
        } else {
            return super.getListeners(listenerType);
        }
        return AWTEventMulticaster.getListeners(l, listenerType);
    }

    // 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},
     * this method invokes the {@code processItemEvent} method.
     * If the event is not an item event,
     * it invokes {@code processEvent} on the superclass.
     * <p>
     * Check box menu items currently support only item events.
     * <p>Note that if the event parameter is {@code null}
     * the behavior is unspecified and may result in an
     * exception.
     *
     * @param        e the event
     * @see          java.awt.event.ItemEvent
     * @see          #processItemEvent
     * @since        1.1
     */
    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} 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:
     * <ul>
     * <li>An {@code ItemListener} object is registered
     * via {@code addItemListener}.
     * <li>Item events are enabled via {@code enableEvents}.
     * </ul>
     * <p>Note that if the event parameter is {@code null}
     * the behavior is unspecified and may result in an
     * exception.
     *
     * @param       e the item event
     * @see         java.awt.event.ItemEvent
     * @see         java.awt.event.ItemListener
     * @see         #addItemListener
     * @see         java.awt.MenuItem#enableEvents
     * @since       1.1
     */
    protected void processItemEvent(ItemEvent e) {
        ItemListener listener = itemListener;
        if (listener != null) {
            listener.itemStateChanged(e);
        }
    }

    /*
     * Post an ItemEvent and toggle state.
     */
    void doMenuEvent(long when, int modifiers) {
        setState(!state);
        Toolkit.getEventQueue().postEvent(
            new ItemEvent(this, ItemEvent.ITEM_STATE_CHANGED,
                          getLabel(),
                          state ? ItemEvent.SELECTED :
                                  ItemEvent.DESELECTED));
    }

    /**
     * Returns a string representing the state of this
     * {@code CheckBoxMenuItem}. This
     * method is intended to be used only for debugging purposes, and the
     * content and format of the returned string may vary between
     * implementations. The returned string may be empty but may not be
     * {@code null}.
     *
     * @return     the parameter string of this check box menu item
     */
    public String paramString() {
        return super.paramString() + ",state=" + state;
    }

    /* Serialization support.
     */

    /**
     * Serialized data version.
     * @serial
     */
    private int checkboxMenuItemSerializedDataVersion = 1;

    /**
     * Writes default serializable fields to stream.  Writes
     * a list of serializable {@code ItemListeners}
     * as optional data.  The non-serializable
     * {@code ItemListeners} are detected and
     * no attempt is made to serialize them.
     *
     * @param  s the {@code ObjectOutputStream} to write
     * @throws IOException if an I/O error occurs
     * @serialData {@code null} terminated sequence of
     *  0 or more pairs; the pair consists of a {@code String}
     *  and an {@code Object}; the {@code String} indicates
     *  the type of object and is one of the following:
     *  {@code itemListenerK} indicating an
     *    {@code ItemListener} object
     *
     * @see AWTEventMulticaster#save(ObjectOutputStream, String, EventListener)
     * @see java.awt.Component#itemListenerK
     * @see #readObject(ObjectInputStream)
     */
    private void writeObject(ObjectOutputStream s)
      throws java.io.IOException
    {
      s.defaultWriteObject();

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

    /**
     * Reads the {@code ObjectInputStream} and if it
     * isn't {@code null} adds a listener to receive
     * item events fired by the {@code Checkbox} menu item.
     * Unrecognized keys or values will be ignored.
     *
     * @param  s the {@code ObjectInputStream} to read
     * @throws ClassNotFoundException if the class of a serialized object could
     *         not be found
     * @throws IOException if an I/O error occurs
     * @serial
     * @see #removeActionListener(ActionListener)
     * @see #addActionListener(ActionListener)
     * @see #writeObject(ObjectOutputStream)
     */
    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();
      }
    }

    /**
     * Initialize JNI field and method IDs
     */
    private static native void initIDs();


/////////////////
// Accessibility support
////////////////

    /**
     * Gets the AccessibleContext associated with this CheckboxMenuItem.
     * For checkbox menu items, the AccessibleContext takes the
     * form of an AccessibleAWTCheckboxMenuItem.
     * A new AccessibleAWTCheckboxMenuItem is created if necessary.
     *
     * @return an AccessibleAWTCheckboxMenuItem that serves as the
     *         AccessibleContext of this CheckboxMenuItem
     * @since 1.3
     */
    public AccessibleContext getAccessibleContext() {
        if (accessibleContext == null) {
            accessibleContext = new AccessibleAWTCheckboxMenuItem();
        }
        return accessibleContext;
    }

    /**
     * Inner class of CheckboxMenuItem used to provide default support for
     * accessibility.  This class is not meant to be used directly by
     * application developers, but is instead meant only to be
     * subclassed by menu component developers.
     * <p>
     * This class implements accessibility support for the
     * {@code CheckboxMenuItem} class.  It provides an implementation
     * of the Java Accessibility API appropriate to checkbox menu item
     * user-interface elements.
     * @since 1.3
     */
    protected class AccessibleAWTCheckboxMenuItem extends AccessibleAWTMenuItem
        implements AccessibleAction, AccessibleValue
    {
        /*
         * JDK 1.3 serialVersionUID
         */
        private static final long serialVersionUID = -1122642964303476L;

        /**
         * Constructs an {@code AccessibleAWTCheckboxMenuItem}.
         */
        protected AccessibleAWTCheckboxMenuItem() {}

        /**
         * Get the AccessibleAction associated with this object.  In the
         * implementation of the Java Accessibility API for this class,
         * return this object, which is responsible for implementing the
         * AccessibleAction interface on behalf of itself.
         *
         * @return this object
         */
        public AccessibleAction getAccessibleAction() {
            return this;
        }

        /**
         * Get the AccessibleValue associated with this object.  In the
         * implementation of the Java Accessibility API for this class,
         * return this object, which is responsible for implementing the
         * AccessibleValue interface on behalf of itself.
         *
         * @return this object
         */
        public AccessibleValue getAccessibleValue() {
            return this;
        }

        /**
         * Returns the number of Actions available in this object.
         * If there is more than one, the first one is the "default"
         * action.
         *
         * @return the number of Actions in this object
         */
        public int getAccessibleActionCount() {
            return 0;  //  To be fully implemented in a future release
        }

        /**
         * Return a description of the specified action of the object.
         *
         * @param i zero-based index of the actions
         */
        public String getAccessibleActionDescription(int i) {
            return null;  //  To be fully implemented in a future release
        }

        /**
         * Perform the specified Action on the object
         *
         * @param i zero-based index of actions
         * @return true if the action was performed; otherwise false.
         */
        public boolean doAccessibleAction(int i) {
            return false;    //  To be fully implemented in a future release
        }

        /**
         * Get the value of this object as a Number.  If the value has not been
         * set, the return value will be null.
         *
         * @return value of the object
         * @see #setCurrentAccessibleValue
         */
        public Number getCurrentAccessibleValue() {
            return null;  //  To be fully implemented in a future release
        }

        /**
         * Set the value of this object as a Number.
         *
         * @return true if the value was set; otherwise false
         * @see #getCurrentAccessibleValue
         */
        public boolean setCurrentAccessibleValue(Number n) {
            return false;  //  To be fully implemented in a future release
        }

        /**
         * Get the minimum value of this object as a Number.
         *
         * @return Minimum value of the object; null if this object does not
         * have a minimum value
         * @see #getMaximumAccessibleValue
         */
        public Number getMinimumAccessibleValue() {
            return null;  //  To be fully implemented in a future release
        }

        /**
         * Get the maximum value of this object as a Number.
         *
         * @return Maximum value of the object; null if this object does not
         * have a maximum value
         * @see #getMinimumAccessibleValue
         */
        public Number getMaximumAccessibleValue() {
            return null;  //  To be fully implemented in a future release
        }

        /**
         * Get the role of this object.
         *
         * @return an instance of AccessibleRole describing the role of the
         * object
         */
        public AccessibleRole getAccessibleRole() {
            return AccessibleRole.CHECK_BOX;
        }

    } // class AccessibleAWTMenuItem

}