simpleselectable.java

jxta_src_2.41b jxta 2.41b 最新版源码 from www.jxta.org

/*
 *
 * $Id: SimpleSelectable.java,v 1.4 2005/09/01 18:00:32 bondolo Exp $
 *
 * Copyright (c) 2004 Sun Microsystems, Inc.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *       Sun Microsystems, Inc. for Project JXTA."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Sun", "Sun Microsystems, Inc.", "JXTA" and "Project JXTA"
 *    must not be used to endorse or promote products derived from this
 *    software without prior written permission. For written
 *    permission, please contact Project JXTA at http://www.jxta.org.
 *
 * 5. Products derived from this software may not be called "JXTA",
 *    nor may "JXTA" appear in their name, without prior written
 *    permission of Sun.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL SUN MICROSYSTEMS OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of Project JXTA.  For more
 * information on Project JXTA, please see
 * <http://www.jxta.org/>.
 *
 * This license is based on the BSD license adopted by the Apache Foundation.
 */

package net.jxta.util;

/**
 * This the interface that all selectable objects expose.<p/>
 *
 * Applications programmers should treat this API as temporary, for now.<p/>
 *
 * A SimpleSelectable object can register SimpleSelector objects so that they are notified whenever this object choses to
 * report a change.<p/>
 *
 * SimpleSelectors are SimpleSelectable, therefore selectors can be selected.<p/>
 *
 * The change notification interface used to notify a selector is actually specified in SimpleSelectable. As a result, certain
 * implementations may also allow to register SimpleSelectables that are not Selectors. Selectors themselves do not allow that.<p/>
 *
 * @see SimpleSelector
 * @see AbstractSimpleSelectable
 **/

public interface SimpleSelectable {

    /**
     * A simple reference object that can be put in a map instead of the one it refers to.
     * SimpleSelectable object often need to be put in maps where distinct objects are to be treated
     * as such, even if they are identical at a semantical level. However, some SimpleSelectable
     * objects may have semantical equals and hashcode methods rather than the identity ones.
     *
     * For that reason, whenever a SimpleSelectable needs to be used as a map or set key, its identity
     * reference should be used instead. All SimpleSelectable can return an identity reference. A given
     * SimpleSelectable always provides the same IdentityReference object. IdentityReference never overloads
     * hashcode and equals in a way that could make different objects be equal or that could provide
     * different results from invocation to invocation.
     **/
    public static class IdentityReference {
        private final Object object;
        /**
         * @return The object that this one refers to.
         **/
        public Object getObject() { return object; }

        /**
         * Creates a new IdentityReference object
         **/
        public IdentityReference(Object object) {
            this.object = object;
        }
    }

    /**
     * @return A canonical IdentityReference for this object.
     * A given SimpleSelectable always provides the same IdentityReference object. An IdentityReference must never overload
     * hashcode and equals in a way that could make different objects be equal or that could provide
     * different results from invocation to invocation.
     **/
    public IdentityReference getIdentityReference();

    /**
     * Registers the given selector with this selectable object. This always causes one change event for this object to be reported
     * through the selector. As a result, when selecting for a condition, it is not necessary to verify whether it has already
     * happened or not; the next call to select will be able to detect it.
     *
     * @param s The SimpleSelector to register
     **/
    public void register(SimpleSelector s);

    /**
     * Unregisters the given selector, so that it is no-longer notified when this object changes. 
     * @param s The SimpleSelector to unregister
     **/
    public void unregister(SimpleSelector s);

    /**
     * This method is invoked when the given selectable object has changed. This permits to cascade selectable objects, so that
     * one reports a change when the other changes, without having to select it. This Also permits to implement this interface by
     * delegating its implementation to a utility class.  <p/> An implementation may do what it wants about it. For example, a
     * {@link SimpleSelector} will report the change to {@link SimpleSelector#select} and invoke {@link
     * AbstractSimpleSelectable#notifyChange()} thereby reporting its own change to cascaded selectors.  Other implementations may
     * only invoke {@link AbstractSimpleSelectable#notifyChange()} or may perform more complex tasks<p/>.
     *
     * @param changedObject the object that has changed.
     * @see AbstractSimpleSelectable
     **/
    public void itemChanged(SimpleSelectable changedObject);
}