menucomponent.java

《移动Agent技术》一书的所有章节源代码。

/*
 * @(#)MenuComponent.java	1.29 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.MenuComponentPeer;
import java.awt.event.ActionEvent;

/**
 * The abstract class <code>MenuComponent</code> is the superclass
 * of all menu-related components. In this respect, the class
 * <code>MenuComponent</code> is analogous to the abstract superclass
 * <code>Component</code> for AWT components.
 * <p>
 * Menu components receive and process AWT events, just as components do,
 * through the method <code>processEvent</code>.
 *
 * @version 	1.29, 08/21/98
 * @author 	Arthur van Hoff
 * @since       JDK1.0
 */
public abstract class MenuComponent implements java.io.Serializable {
    transient MenuComponentPeer peer;
    transient MenuContainer parent;
    Font font;
    private String name;
    private boolean nameExplicitlySet = false;

    boolean newEventsOnly = false;

    /*
     * Internal constants for serialization
     */
    final static String actionListenerK = Component.actionListenerK;
    final static String itemListenerK = Component.itemListenerK;

    /*
     * JDK 1.1 serialVersionUID
     */
    private static final long serialVersionUID = -4536902356223894379L;

    /**
     * Construct a name for this MenuComponent.  Called by getName() when
     * the name is null.
     */
    String constructComponentName() {
	return null; // For strict compliance with prior JDKs, a MenuComponent
	             // that doesn't set its name should return null from
	             // getName()
    }

    /**
     * Gets the name of the menu component.
     * @return        the name of the menu component.
     * @see           java.awt.MenuComponent#setName(java.lang.String)
     * @since         JDK1.1
     */
    public String getName() {
	if (name == null && !nameExplicitlySet) {
	    synchronized(this) {
		if (name == null && !nameExplicitlySet) {
		    name = constructComponentName();
		}
	    }
	}
        return name;
    }

    /**
     * Sets the name of the component to the specified string.
     * @param         name    the name of the menu component.
     * @see           java.awt.MenuComponent#getName
     * @since         JDK1.1
     */
    public void setName(String name) {
	synchronized(this) {
	    this.name = name;
	    nameExplicitlySet = true;
	}
    }

    /**
     * Returns the parent container for this menu component.
     * @return    the menu component containing this menu component,
     *                 or <code>null</code> if this menu component
     *                 is the outermost component, the menu bar itself.
     * @since     JDK1.0
     */
    public MenuContainer getParent() {
	return parent;
    }

    /**
     * @deprecated As of JDK version 1.1,
     * programs should not directly manipulate peers.
     */
    public MenuComponentPeer getPeer() {
	return peer;
    }

    /**
     * Gets the font used for this menu component.
     * @return   the font used in this menu component, if there is one;
     *                  <code>null</code> otherwise.
     * @see     java.awt.MenuComponent#setFont
     * @since   JDK1.0
     */
    public Font getFont() {
	Font font = this.font;
	if (font != null) {
	    return font;
	}
	MenuContainer parent = this.parent;
	if (parent != null) {
	    return parent.getFont();
	}
	return null;
    }

    /**
     * Sets the font to be used for this menu component to the specified
     * font. This font is also used by all subcomponents of this menu
     * component, unless those subcomponents specify a different font.
     * @param     f   the font to be set.
     * @see       java.awt.MenuComponent#getFont
     * @since     JDK1.0
     */
    public void setFont(Font f) {
	font = f;
    }

    /**
     * Removes the menu component's peer.  The peer allows us to modify the
     * appearance of the menu component without changing the functionality of
     * the menu component.
     */
    public void removeNotify() {
        synchronized(getTreeLock()) {
	    MenuComponentPeer p = (MenuComponentPeer)this.peer;
	    if (p != null) {
                Toolkit.getEventQueue().removeSourceEvents(this);
	        this.peer = null;
	        p.dispose();
	    }
        }
    }

    /**
     * Posts the specified event to the menu.
     * This method is part of the Java&nbsp;1.0 event system
     * and it is maintained only for backwards compatibility.
     * Its use is discouraged, and it may not be supported
     * in the future.
     * @param evt the event which is to take place
     * @deprecated As of JDK version 1.1,
     * replaced by <code>dispatchEvent(AWTEvent)</code>.
     * @since JDK1.0
     */
    public boolean postEvent(Event evt) {
	MenuContainer parent = this.parent;
	if (parent != null) {
	    parent.postEvent(evt);
	}
	return false;
    }

    /*
     * Delivers an event to this component or one of its sub components.
     * @param e the event
     */
    public final void dispatchEvent(AWTEvent e) {
        dispatchEventImpl(e);
    }

    void dispatchEventImpl(AWTEvent e) {
        if (newEventsOnly ||
            (parent != null && parent instanceof MenuComponent &&
             ((MenuComponent)parent).newEventsOnly)) {
            if (eventEnabled(e)) {
                processEvent(e);
            } else if (e instanceof ActionEvent && parent != null) {
                ((MenuComponent)parent).dispatchEvent(new ActionEvent(parent,
                                         e.getID(),
                                         ((ActionEvent)e).getActionCommand()));
            }

        } else { // backward compatibility
            Event olde = e.convertToOld();
            if (olde != null) {
                postEvent(olde);
            }
        }
    }

    // REMIND: remove when filtering is done at lower level
    boolean eventEnabled(AWTEvent e) {
        return false;
    }
    /**
     * Processes events occurring on this menu component.
     * @param e the event
     * @since JDK1.1
     */
    protected void processEvent(AWTEvent e) {
    }

    /**
     * Returns the parameter string representing the state of this
     * menu component. This string is useful for debugging.
     * @return     the parameter string of this menu component.
     * @since      JDK1.0
     */
    protected String paramString() {
	String thisName = getName();
	return (thisName != null? thisName : "");
    }

    /**
     * Returns a representation of this menu component as a string.
     * @return  a string representation of this menu component.
     * @since     JDK1.0
     */
    public String toString() {
	return getClass().getName() + "[" + paramString() + "]";
    }

    /**
     * Gets this component's locking object (the object that owns the thread
     * sychronization monitor) for AWT component-tree and layout
     * operations.
     * @return This component's locking object.
     */
    protected final Object getTreeLock() {
	return Component.LOCK;
    }

}