Java example source code file (MenuBar.java)

This example Java source code file (MenuBar.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

accessibleawtmenubar, accessiblecontext, awt, classnotfoundexception, deprecated, enumeration, event, headlessexception, ioexception, menu, menubarpeer, menucomponent, menuitem, menushortcut, string, util, vector

The MenuBar.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.io.IOException;
import java.io.ObjectInputStream;
import java.util.Vector;
import java.util.Enumeration;
import sun.awt.AWTAccessor;
import java.awt.peer.MenuBarPeer;
import java.awt.event.KeyEvent;
import javax.accessibility.*;

/**
 * The <code>MenuBar class encapsulates the platform's
 * concept of a menu bar bound to a frame. In order to associate
 * the menu bar with a <code>Frame object, call the
 * frame's <code>setMenuBar method.
 * <p>
 * <A NAME="mbexample">
 * This is what a menu bar might look like:
 * <p>
 * <img src="doc-files/MenuBar-1.gif"
 * alt="Diagram of MenuBar containing 2 menus: Examples and Options.
 * Examples menu is expanded showing items: Basic, Simple, Check, and More Examples."
 * style="float:center; margin: 7px 10px;">
 * <p>
 * A menu bar handles keyboard shortcuts for menu items, passing them
 * along to its child menus.
 * (Keyboard shortcuts, which are optional, provide the user with
 * an alternative to the mouse for invoking a menu item and the
 * action that is associated with it.)
 * Each menu item can maintain an instance of <code>MenuShortcut.
 * The <code>MenuBar class defines several methods,
 * {@link MenuBar#shortcuts} and
 * {@link MenuBar#getShortcutMenuItem}
 * that retrieve information about the shortcuts a given
 * menu bar is managing.
 *
 * @author Sami Shaio
 * @see        java.awt.Frame
 * @see        java.awt.Frame#setMenuBar(java.awt.MenuBar)
 * @see        java.awt.Menu
 * @see        java.awt.MenuItem
 * @see        java.awt.MenuShortcut
 * @since      JDK1.0
 */
public class MenuBar extends MenuComponent implements MenuContainer, Accessible {

    static {
        /* ensure that the necessary native libraries are loaded */
        Toolkit.loadLibraries();
        if (!GraphicsEnvironment.isHeadless()) {
            initIDs();
        }
        AWTAccessor.setMenuBarAccessor(
            new AWTAccessor.MenuBarAccessor() {
                public Menu getHelpMenu(MenuBar menuBar) {
                    return menuBar.helpMenu;
                }

                public Vector<Menu> getMenus(MenuBar menuBar) {
                    return menuBar.menus;
                }
            });
    }

    /**
     * This field represents a vector of the
     * actual menus that will be part of the MenuBar.
     *
     * @serial
     * @see #countMenus()
     */
    Vector<Menu> menus = new Vector<>();

    /**
     * This menu is a special menu dedicated to
     * help.  The one thing to note about this menu
     * is that on some platforms it appears at the
     * right edge of the menubar.
     *
     * @serial
     * @see #getHelpMenu()
     * @see #setHelpMenu(Menu)
     */
    Menu helpMenu;

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

    /*
     * JDK 1.1 serialVersionUID
     */
     private static final long serialVersionUID = -4930327919388951260L;

    /**
     * Creates a new menu bar.
     * @exception HeadlessException if GraphicsEnvironment.isHeadless()
     * returns true.
     * @see java.awt.GraphicsEnvironment#isHeadless
     */
    public MenuBar() throws HeadlessException {
    }

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

    /**
     * Creates the menu bar's peer.  The peer allows us to change the
     * appearance of the menu bar without changing any of the menu bar's
     * functionality.
     */
    public void addNotify() {
        synchronized (getTreeLock()) {
            if (peer == null)
                peer = Toolkit.getDefaultToolkit().createMenuBar(this);

            int nmenus = getMenuCount();
            for (int i = 0 ; i < nmenus ; i++) {
                getMenu(i).addNotify();
            }
        }
    }

    /**
     * Removes the menu bar's peer.  The peer allows us to change the
     * appearance of the menu bar without changing any of the menu bar's
     * functionality.
     */
    public void removeNotify() {
        synchronized (getTreeLock()) {
            int nmenus = getMenuCount();
            for (int i = 0 ; i < nmenus ; i++) {
                getMenu(i).removeNotify();
            }
            super.removeNotify();
        }
    }

    /**
     * Gets the help menu on the menu bar.
     * @return    the help menu on this menu bar.
     */
    public Menu getHelpMenu() {
        return helpMenu;
    }

    /**
     * Sets the specified menu to be this menu bar's help menu.
     * If this menu bar has an existing help menu, the old help menu is
     * removed from the menu bar, and replaced with the specified menu.
     * @param m    the menu to be set as the help menu
     */
    public void setHelpMenu(Menu m) {
        synchronized (getTreeLock()) {
            if (helpMenu == m) {
                return;
            }
            if (helpMenu != null) {
                remove(helpMenu);
            }
            if (m.parent != this) {
                add(m);
            }
            helpMenu = m;
            if (m != null) {
                m.isHelpMenu = true;
                m.parent = this;
                MenuBarPeer peer = (MenuBarPeer)this.peer;
                if (peer != null) {
                    if (m.peer == null) {
                        m.addNotify();
                    }
                    peer.addHelpMenu(m);
                }
            }
        }
    }

    /**
     * Adds the specified menu to the menu bar.
     * If the menu has been part of another menu bar,
     * removes it from that menu bar.
     *
     * @param        m   the menu to be added
     * @return       the menu added
     * @see          java.awt.MenuBar#remove(int)
     * @see          java.awt.MenuBar#remove(java.awt.MenuComponent)
     */
    public Menu add(Menu m) {
        synchronized (getTreeLock()) {
            if (m.parent != null) {
                m.parent.remove(m);
            }
            menus.addElement(m);
            m.parent = this;

            MenuBarPeer peer = (MenuBarPeer)this.peer;
            if (peer != null) {
                if (m.peer == null) {
                    m.addNotify();
                }
                peer.addMenu(m);
            }
            return m;
        }
    }

    /**
     * Removes the menu located at the specified
     * index from this menu bar.
     * @param        index   the position of the menu to be removed.
     * @see          java.awt.MenuBar#add(java.awt.Menu)
     */
    public void remove(int index) {
        synchronized (getTreeLock()) {
            Menu m = getMenu(index);
            menus.removeElementAt(index);
            MenuBarPeer peer = (MenuBarPeer)this.peer;
            if (peer != null) {
                m.removeNotify();
                m.parent = null;
                peer.delMenu(index);
            }
        }
    }

    /**
     * Removes the specified menu component from this menu bar.
     * @param        m the menu component to be removed.
     * @see          java.awt.MenuBar#add(java.awt.Menu)
     */
    public void remove(MenuComponent m) {
        synchronized (getTreeLock()) {
            int index = menus.indexOf(m);
            if (index >= 0) {
                remove(index);
            }
        }
    }

    /**
     * Gets the number of menus on the menu bar.
     * @return     the number of menus on the menu bar.
     * @since      JDK1.1
     */
    public int getMenuCount() {
        return countMenus();
    }

    /**
     * @deprecated As of JDK version 1.1,
     * replaced by <code>getMenuCount().
     */
    @Deprecated
    public int countMenus() {
        return getMenuCountImpl();
    }

    /*
     * This is called by the native code, so client code can't
     * be called on the toolkit thread.
     */
    final int getMenuCountImpl() {
        return menus.size();
    }

    /**
     * Gets the specified menu.
     * @param      i the index position of the menu to be returned.
     * @return     the menu at the specified index of this menu bar.
     */
    public Menu getMenu(int i) {
        return getMenuImpl(i);
    }

    /*
     * This is called by the native code, so client code can't
     * be called on the toolkit thread.
     */
    final Menu getMenuImpl(int i) {
        return menus.elementAt(i);
    }

    /**
     * Gets an enumeration of all menu shortcuts this menu bar
     * is managing.
     * @return      an enumeration of menu shortcuts that this
     *                      menu bar is managing.
     * @see         java.awt.MenuShortcut
     * @since       JDK1.1
     */
    public synchronized Enumeration<MenuShortcut> shortcuts() {
        Vector<MenuShortcut> shortcuts = new Vector<>();
        int nmenus = getMenuCount();
        for (int i = 0 ; i < nmenus ; i++) {
            Enumeration<MenuShortcut> e = getMenu(i).shortcuts();
            while (e.hasMoreElements()) {
                shortcuts.addElement(e.nextElement());
            }
        }
        return shortcuts.elements();
    }

    /**
     * Gets the instance of <code>MenuItem associated
     * with the specified <code>MenuShortcut object,
     * or <code>null if none of the menu items being managed
     * by this menu bar is associated with the specified menu
     * shortcut.
     * @param        s the specified menu shortcut.
     * @see          java.awt.MenuItem
     * @see          java.awt.MenuShortcut
     * @since        JDK1.1
     */
     public MenuItem getShortcutMenuItem(MenuShortcut s) {
        int nmenus = getMenuCount();
        for (int i = 0 ; i < nmenus ; i++) {
            MenuItem mi = getMenu(i).getShortcutMenuItem(s);
            if (mi != null) {
                return mi;
            }
        }
        return null;  // MenuShortcut wasn't found
     }

    /*
     * Post an ACTION_EVENT to the target of the MenuPeer
     * associated with the specified keyboard event (on
     * keydown).  Returns true if there is an associated
     * keyboard event.
     */
    boolean handleShortcut(KeyEvent e) {
        // Is it a key event?
        int id = e.getID();
        if (id != KeyEvent.KEY_PRESSED && id != KeyEvent.KEY_RELEASED) {
            return false;
        }

        // Is the accelerator modifier key pressed?
        int accelKey = Toolkit.getDefaultToolkit().getMenuShortcutKeyMask();
        if ((e.getModifiers() & accelKey) == 0) {
            return false;
        }

        // Pass MenuShortcut on to child menus.
        int nmenus = getMenuCount();
        for (int i = 0 ; i < nmenus ; i++) {
            Menu m = getMenu(i);
            if (m.handleShortcut(e)) {
                return true;
            }
        }
        return false;
    }

    /**
     * Deletes the specified menu shortcut.
     * @param     s the menu shortcut to delete.
     * @since     JDK1.1
     */
    public void deleteShortcut(MenuShortcut s) {
        int nmenus = getMenuCount();
        for (int i = 0 ; i < nmenus ; i++) {
            getMenu(i).deleteShortcut(s);
        }
    }

    /* Serialization support.  Restore the (transient) parent
     * fields of Menubar menus here.
     */

    /**
     * The MenuBar's serialized data version.
     *
     * @serial
     */
    private int menuBarSerializedDataVersion = 1;

    /**
     * Writes default serializable fields to stream.
     *
     * @param s the <code>ObjectOutputStream to write
     * @see AWTEventMulticaster#save(ObjectOutputStream, String, EventListener)
     * @see #readObject(java.io.ObjectInputStream)
     */
    private void writeObject(java.io.ObjectOutputStream s)
      throws java.lang.ClassNotFoundException,
             java.io.IOException
    {
      s.defaultWriteObject();
    }

    /**
     * Reads the <code>ObjectInputStream.
     * Unrecognized keys or values will be ignored.
     *
     * @param s the <code>ObjectInputStream to read
     * @exception HeadlessException if
     *   <code>GraphicsEnvironment.isHeadless returns
     *   <code>true
     * @see java.awt.GraphicsEnvironment#isHeadless
     * @see #writeObject(java.io.ObjectOutputStream)
     */
    private void readObject(ObjectInputStream s)
      throws ClassNotFoundException, IOException, HeadlessException
    {
      // HeadlessException will be thrown from MenuComponent's readObject
      s.defaultReadObject();
      for (int i = 0; i < menus.size(); i++) {
        Menu m = menus.elementAt(i);
        m.parent = this;
      }
    }

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


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

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

    /**
     * Defined in MenuComponent. Overridden here.
     */
    int getAccessibleChildIndex(MenuComponent child) {
        return menus.indexOf(child);
    }

    /**
     * Inner class of MenuBar 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>MenuBar class.  It provides an implementation of the
     * Java Accessibility API appropriate to menu bar user-interface elements.
     * @since 1.3
     */
    protected class AccessibleAWTMenuBar extends AccessibleAWTMenuComponent
    {
        /*
         * JDK 1.3 serialVersionUID
         */
        private static final long serialVersionUID = -8577604491830083815L;

        /**
         * Get the role of this object.
         *
         * @return an instance of AccessibleRole describing the role of the
         * object
         * @since 1.4
         */
        public AccessibleRole getAccessibleRole() {
            return AccessibleRole.MENU_BAR;
        }

    } // class AccessibleAWTMenuBar

}