Java example source code file (MenuItem.java)

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accessibleaction, accessibleawtmenuitem, accessiblevalue, actionevent, actionlistener, awt, deprecated, event, eventlistener, headlessexception, ioexception, menuitem, menuitempeer, menushortcut, number, string, util

The MenuItem.java Java example source code

/*
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 * 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
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package java.awt;

import java.awt.peer.MenuItemPeer;
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;

/**
 * All items in a menu must belong to the class
 * <code>MenuItem, or one of its subclasses.
 * <p>
 * The default <code>MenuItem object embodies
 * a simple labeled menu item.
 * <p>
 * This picture of a menu bar shows five menu items:
 * <IMG SRC="doc-files/MenuBar-1.gif" alt="The following text describes this graphic."
 * style="float:center; margin: 7px 10px;">
 * <br style="clear:left;">
 * The first two items are simple menu items, labeled
 * <code>"Basic" and "Simple".
 * Following these two items is a separator, which is itself
 * a menu item, created with the label <code>"-".
 * Next is an instance of <code>CheckboxMenuItem
 * labeled <code>"Check". The final menu item is a
 * submenu labeled <code>"More Examples",
 * and this submenu is an instance of <code>Menu.
 * <p>
 * When a menu item is selected, AWT sends an action event to
 * the menu item. Since the event is an
 * instance of <code>ActionEvent, the processEvent
 * method examines the event and passes it along to
 * <code>processActionEvent. The latter method redirects the
 * event to any <code>ActionListener objects that have
 * registered an interest in action events generated by this
 * menu item.
 * <P>
 * Note that the subclass <code>Menu overrides this behavior and
 * does not send any event to the frame until one of its subitems is
 * selected.
 *
 * @author Sami Shaio
 */
public class MenuItem extends MenuComponent implements Accessible {

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

        AWTAccessor.setMenuItemAccessor(
            new AWTAccessor.MenuItemAccessor() {
                public boolean isEnabled(MenuItem item) {
                    return item.enabled;
                }

                public String getLabel(MenuItem item) {
                    return item.label;
                }

                public MenuShortcut getShortcut(MenuItem item) {
                    return item.shortcut;
                }

                public String getActionCommandImpl(MenuItem item) {
                    return item.getActionCommandImpl();
                }

                public boolean isItemEnabled(MenuItem item) {
                    return item.isItemEnabled();
                }
            });
    }

    /**
     * A value to indicate whether a menu item is enabled
     * or not.  If it is enabled, <code>enabled will
     * be set to true.  Else <code>enabled will
     * be set to false.
     *
     * @serial
     * @see #isEnabled()
     * @see #setEnabled(boolean)
     */
    boolean enabled = true;

    /**
     * <code>label is the label of a menu item.
     * It can be any string.
     *
     * @serial
     * @see #getLabel()
     * @see #setLabel(String)
     */
    String label;

    /**
     * This field indicates the command tha has been issued
     * by a  particular menu item.
     * By default the <code>actionCommand
     * is the label of the menu item, unless it has been
     * set using setActionCommand.
     *
     * @serial
     * @see #setActionCommand(String)
     * @see #getActionCommand()
     */
    String actionCommand;

    /**
     * The eventMask is ONLY set by subclasses via enableEvents.
     * The mask should NOT be set when listeners are registered
     * so that we can distinguish the difference between when
     * listeners request events and subclasses request them.
     *
     * @serial
     */
    long eventMask;

    transient ActionListener actionListener;

    /**
     * A sequence of key stokes that ia associated with
     * a menu item.
     * Note :in 1.1.2 you must use setActionCommand()
     * on a menu item in order for its shortcut to
     * work.
     *
     * @serial
     * @see #getShortcut()
     * @see #setShortcut(MenuShortcut)
     * @see #deleteShortcut()
     */
    private MenuShortcut shortcut = null;

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

    /*
     * JDK 1.1 serialVersionUID
     */
    private static final long serialVersionUID = -21757335363267194L;

    /**
     * Constructs a new MenuItem with an empty label and no keyboard
     * shortcut.
     * @exception HeadlessException if GraphicsEnvironment.isHeadless()
     * returns true.
     * @see java.awt.GraphicsEnvironment#isHeadless
     * @since    JDK1.1
     */
    public MenuItem() throws HeadlessException {
        this("", null);
    }

    /**
     * Constructs a new MenuItem with the specified label
     * and no keyboard shortcut. Note that use of "-" in
     * a label is reserved to indicate a separator between
     * menu items. By default, all menu items except for
     * separators are enabled.
     * @param       label the label for this menu item.
     * @exception HeadlessException if GraphicsEnvironment.isHeadless()
     * returns true.
     * @see java.awt.GraphicsEnvironment#isHeadless
     * @since       JDK1.0
     */
    public MenuItem(String label) throws HeadlessException {
        this(label, null);
    }

    /**
     * Create a menu item with an associated keyboard shortcut.
     * Note that use of "-" in a label is reserved to indicate
     * a separator between menu items. By default, all menu
     * items except for separators are enabled.
     * @param       label the label for this menu item.
     * @param       s the instance of <code>MenuShortcut
     *                       associated with this menu item.
     * @exception HeadlessException if GraphicsEnvironment.isHeadless()
     * returns true.
     * @see java.awt.GraphicsEnvironment#isHeadless
     * @since       JDK1.1
     */
    public MenuItem(String label, MenuShortcut s) throws HeadlessException {
        this.label = label;
        this.shortcut = s;
    }

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

    /**
     * Creates the menu item's peer.  The peer allows us to modify the
     * appearance of the menu item without changing its functionality.
     */
    public void addNotify() {
        synchronized (getTreeLock()) {
            if (peer == null)
                peer = Toolkit.getDefaultToolkit().createMenuItem(this);
        }
    }

    /**
     * Gets the label for this menu item.
     * @return  the label of this menu item, or <code>null
                       if this menu item has no label.
     * @see     java.awt.MenuItem#setLabel
     * @since   JDK1.0
     */
    public String getLabel() {
        return label;
    }

    /**
     * Sets the label for this menu item to the specified label.
     * @param     label   the new label, or <code>null for no label.
     * @see       java.awt.MenuItem#getLabel
     * @since     JDK1.0
     */
    public synchronized void setLabel(String label) {
        this.label = label;
        MenuItemPeer peer = (MenuItemPeer)this.peer;
        if (peer != null) {
            peer.setLabel(label);
        }
    }

    /**
     * Checks whether this menu item is enabled.
     * @see        java.awt.MenuItem#setEnabled
     * @since      JDK1.0
     */
    public boolean isEnabled() {
        return enabled;
    }

    /**
     * Sets whether or not this menu item can be chosen.
     * @param      b  if <code>true, enables this menu item;
     *                       if <code>false, disables it.
     * @see        java.awt.MenuItem#isEnabled
     * @since      JDK1.1
     */
    public synchronized void setEnabled(boolean b) {
        enable(b);
    }

    /**
     * @deprecated As of JDK version 1.1,
     * replaced by <code>setEnabled(boolean).
     */
    @Deprecated
    public synchronized void enable() {
        enabled = true;
        MenuItemPeer peer = (MenuItemPeer)this.peer;
        if (peer != null) {
            peer.setEnabled(true);
        }
    }

    /**
     * @deprecated As of JDK version 1.1,
     * replaced by <code>setEnabled(boolean).
     */
    @Deprecated
    public void enable(boolean b) {
        if (b) {
            enable();
        } else {
            disable();
        }
    }

    /**
     * @deprecated As of JDK version 1.1,
     * replaced by <code>setEnabled(boolean).
     */
    @Deprecated
    public synchronized void disable() {
        enabled = false;
        MenuItemPeer peer = (MenuItemPeer)this.peer;
        if (peer != null) {
            peer.setEnabled(false);
        }
    }

    /**
     * Get the <code>MenuShortcut object associated with this
     * menu item,
     * @return      the menu shortcut associated with this menu item,
     *                   or <code>null if none has been specified.
     * @see         java.awt.MenuItem#setShortcut
     * @since       JDK1.1
     */
    public MenuShortcut getShortcut() {
        return shortcut;
    }

    /**
     * Set the <code>MenuShortcut object associated with this
     * menu item. If a menu shortcut is already associated with
     * this menu item, it is replaced.
     * @param       s  the menu shortcut to associate
     *                           with this menu item.
     * @see         java.awt.MenuItem#getShortcut
     * @since       JDK1.1
     */
    public void setShortcut(MenuShortcut s) {
        shortcut = s;
        MenuItemPeer peer = (MenuItemPeer)this.peer;
        if (peer != null) {
            peer.setLabel(label);
        }
    }

    /**
     * Delete any <code>MenuShortcut object associated
     * with this menu item.
     * @since      JDK1.1
     */
    public void deleteShortcut() {
        shortcut = null;
        MenuItemPeer peer = (MenuItemPeer)this.peer;
        if (peer != null) {
            peer.setLabel(label);
        }
    }

    /*
     * Delete a matching MenuShortcut associated with this MenuItem.
     * Used when iterating Menus.
     */
    void deleteShortcut(MenuShortcut s) {
        if (s.equals(shortcut)) {
            shortcut = null;
            MenuItemPeer peer = (MenuItemPeer)this.peer;
            if (peer != null) {
                peer.setLabel(label);
            }
        }
    }

    /*
     * The main goal of this method is to post an appropriate event
     * to the event queue when menu shortcut is pressed. However,
     * in subclasses this method may do more than just posting
     * an event.
     */
    void doMenuEvent(long when, int modifiers) {
        Toolkit.getEventQueue().postEvent(
            new ActionEvent(this, ActionEvent.ACTION_PERFORMED,
                            getActionCommand(), when, modifiers));
    }

    /*
     * Returns true if the item and all its ancestors are
     * enabled, false otherwise
     */
    private final boolean isItemEnabled() {
        // Fix For 6185151: Menu shortcuts of all menuitems within a menu
        // should be disabled when the menu itself is disabled
        if (!isEnabled()) {
            return false;
        }
        MenuContainer container = getParent_NoClientCode();
        do {
            if (!(container instanceof Menu)) {
                return true;
            }
            Menu menu = (Menu)container;
            if (!menu.isEnabled()) {
                return false;
            }
            container = menu.getParent_NoClientCode();
        } while (container != null);
        return true;
    }

    /*
     * Post an ActionEvent to the target (on
     * keydown) and the item is enabled.
     * Returns true if there is an associated shortcut.
     */
    boolean handleShortcut(KeyEvent e) {
        MenuShortcut s = new MenuShortcut(e.getKeyCode(),
                             (e.getModifiers() & InputEvent.SHIFT_MASK) > 0);
        MenuShortcut sE = new MenuShortcut(e.getExtendedKeyCode(),
                             (e.getModifiers() & InputEvent.SHIFT_MASK) > 0);
        // Fix For 6185151: Menu shortcuts of all menuitems within a menu
        // should be disabled when the menu itself is disabled
        if ((s.equals(shortcut) || sE.equals(shortcut)) && isItemEnabled()) {
            // MenuShortcut match -- issue an event on keydown.
            if (e.getID() == KeyEvent.KEY_PRESSED) {
                doMenuEvent(e.getWhen(), e.getModifiers());
            } else {
                // silently eat key release.
            }
            return true;
        }
        return false;
    }

    MenuItem getShortcutMenuItem(MenuShortcut s) {
        return (s.equals(shortcut)) ? this : null;
    }

    /**
     * Enables event delivery to this menu item for events
     * to be defined by the specified event mask parameter
     * <p>
     * Since event types are automatically enabled when a listener for
     * that type is added to the menu item, this method only needs
     * to be invoked by subclasses of <code>MenuItem which desire to
     * have the specified event types delivered to <code>processEvent
     * regardless of whether a listener is registered.
     *
     * @param       eventsToEnable the event mask defining the event types
     * @see         java.awt.MenuItem#processEvent
     * @see         java.awt.MenuItem#disableEvents
     * @see         java.awt.Component#enableEvents
     * @since       JDK1.1
     */
    protected final void enableEvents(long eventsToEnable) {
        eventMask |= eventsToEnable;
        newEventsOnly = true;
    }

    /**
     * Disables event delivery to this menu item for events
     * defined by the specified event mask parameter.
     *
     * @param       eventsToDisable the event mask defining the event types
     * @see         java.awt.MenuItem#processEvent
     * @see         java.awt.MenuItem#enableEvents
     * @see         java.awt.Component#disableEvents
     * @since       JDK1.1
     */
    protected final void disableEvents(long eventsToDisable) {
        eventMask &= ~eventsToDisable;
    }

    /**
     * Sets the command name of the action event that is fired
     * by this menu item.
     * <p>
     * By default, the action command is set to the label of
     * the menu item.
     * @param       command   the action command to be set
     *                                for this menu item.
     * @see         java.awt.MenuItem#getActionCommand
     * @since       JDK1.1
     */
    public void setActionCommand(String command) {
        actionCommand = command;
    }

    /**
     * Gets the command name of the action event that is fired
     * by this menu item.
     * @see         java.awt.MenuItem#setActionCommand
     * @since       JDK1.1
     */
    public String getActionCommand() {
        return getActionCommandImpl();
    }

    // This is final so it can be called on the Toolkit thread.
    final String getActionCommandImpl() {
        return (actionCommand == null? label : actionCommand);
    }

    /**
     * Adds the specified action listener to receive action events
     * from this 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 action listener.
     * @see        #removeActionListener
     * @see        #getActionListeners
     * @see        java.awt.event.ActionEvent
     * @see        java.awt.event.ActionListener
     * @since      JDK1.1
     */
    public synchronized void addActionListener(ActionListener l) {
        if (l == null) {
            return;
        }
        actionListener = AWTEventMulticaster.add(actionListener, l);
        newEventsOnly = true;
    }

    /**
     * Removes the specified action listener so it no longer receives
     * action events from this 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 action listener.
     * @see        #addActionListener
     * @see        #getActionListeners
     * @see        java.awt.event.ActionEvent
     * @see        java.awt.event.ActionListener
     * @since      JDK1.1
     */
    public synchronized void removeActionListener(ActionListener l) {
        if (l == null) {
            return;
        }
        actionListener = AWTEventMulticaster.remove(actionListener, l);
    }

    /**
     * Returns an array of all the action listeners
     * registered on this menu item.
     *
     * @return all of this menu item's <code>ActionListeners
     *         or an empty array if no action
     *         listeners are currently registered
     *
     * @see        #addActionListener
     * @see        #removeActionListener
     * @see        java.awt.event.ActionEvent
     * @see        java.awt.event.ActionListener
     * @since 1.4
     */
    public synchronized ActionListener[] getActionListeners() {
        return getListeners(ActionListener.class);
    }

    /**
     * Returns an array of all the objects currently registered
     * as <code>FooListeners
     * upon this <code>MenuItem.
     * <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>MenuItem m
     * for its action listeners with the following code:
     *
     * <pre>ActionListener[] als = (ActionListener[])(m.getListeners(ActionListener.class));