menuitem.java

《移动Agent技术》一书的所有章节源代码。

/*
 * @(#)MenuItem.java	1.48 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.MenuItemPeer;
import java.awt.event.*;
import java.io.ObjectOutputStream;
import java.io.ObjectInputStream;
import java.io.IOException;


/**
 * All items in a menu must belong to the class
 * <code>MenuItem</code>, or one of its subclasses.
 * <p>
 * The default <code>MenuItem</code> object embodies
 * a simple labeled menu item.
 * <p>
 * This picture of a menu bar shows five menu items:
 * <IMG SRC="images-awt/MenuBar-1.gif"
 * ALIGN=CENTER HSPACE=10 VSPACE=7>
 * <br CLEAR=LEFT>
 * The first two items are simple menu items, labeled
 * <code>"Basic"</code> and <code>"Simple"</code>.
 * Following these two items is a separator, which is itself
 * a menu item, created with the label <code>"-"</code>.
 * Next is an instance of <code>CheckboxMenuItem</code>
 * labeled <code>"Check"</code>. The final menu item is a
 * submenu labeled <code>"More&nbsp;Examples"</code>,
 * and this submenu is an instance of <code>Menu</code>.
 * <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</code>, the <code>processEvent</code>
 * method examines the event and passes it along to
 * <code>processActionEvent</code>. The latter method redirects the
 * event to any <code>ActionListener</code> objects that have
 * registered an interest in action events generated by this
 * menu item.
 * <P>
 * Note that the subclass <code>Menu</code> overrides this behavior and
 * does not send any event to the frame until one of its subitems is
 * selected.
 *
 * @version 1.48, 08/21/98
 * @author Sami Shaio
 */
public class MenuItem extends MenuComponent {
    boolean enabled = true;
    String label;
    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.
    long eventMask;

    transient ActionListener actionListener;

    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.
     * @since    JDK1.1
     */
    public MenuItem() {
	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.
     * @since       JDK1.0
     */
    public MenuItem(String label) {
	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</code>
     *                       associated with this menu item.
     * @since       JDK1.1
     */
    public MenuItem(String label, MenuShortcut s) {
	this.label = label;
        this.shortcut = s;
    }

    /**
     * Construct a name for this MenuComponent.  Called by getName() when
     * the name is null.
     */
    String constructComponentName() {
        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</code>
                       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</code> 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</code>, enables this menu item;
     *                       if <code>false</code>, 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)</code>.
     */
    public synchronized void enable() {
	enabled = true;
	MenuItemPeer peer = (MenuItemPeer)this.peer;
	if (peer != null) {
	    peer.enable();
	}
    }

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

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

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

    /**
     * Set the <code>MenuShortcut</code> 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;
        synchronized (getTreeLock()) {			/*ibm.3202*/
	    MenuItemPeer peer = (MenuItemPeer)this.peer;
	    if (peer != null) {
	        peer.setLabel(label);
	    }