dynamicenumeration.java

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

/*
 *
 * $Id: DynamicEnumeration.java,v 1.2 2003/05/30 17:22:25 bondolo Exp $
 *
 * Copyright (c) 2002 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.impl.util;

import java.util.ArrayList;
import java.util.Enumeration;
import java.util.List;

import java.util.NoSuchElementException;

/**
 *  A dynamic {@link java.util.Enumeration} which allows items to added to the
 *  enumeration while it is in use. This is mostly intended for use with
 *  {@link java.io.SequenceInputStream}.
 *
 *  <p/>This class is entirely thread safe. Attempting to use the enumeration
 *  and to add objects from a single thread is not recommended, as it may
 *  deadlock the thread.
 *
 **/
public class DynamicEnumeration implements Enumeration {
    private List sequence = new ArrayList();
    
    private volatile boolean closed = false;
    
    /**
     * Creates a new instance of DynamicEnumeration
     **/
    public DynamicEnumeration( ) {
    }
    
    /**
     * Creates a new instance of DynamicEnumeration
     **/
    public DynamicEnumeration( List initial ) {
        sequence.addAll( initial );
    }
    
    /**
     *  {@inheritDoc}
     *
     *  <p/>If the Enumeration has not been closed we may have to block until we
     *  have a stream to return.
     **/
    public boolean hasMoreElements() {
        while( !closed ) {
            synchronized( sequence ) {
                if( !sequence.isEmpty() )
                    return true;
                
                try {
                    sequence.wait();
                } catch( InterruptedException woken ) {
                    Thread.interrupted();
                }
            }
        }
        
        return false;
    }
    
    /**
     *  {@inheritDoc}
     *
     *  <p/>If the Enumeration has not been closed we may have to block until we
     *  have a stream to return.
     **/
    public synchronized Object nextElement() {
        while( !closed ) {
            synchronized( sequence ) {
                if( sequence.isEmpty() ) {
                    try {
                        sequence.wait();
                    } catch( InterruptedException woken ) {
                        Thread.interrupted();
                    }
                    continue;
                }
                
                Object result = sequence.remove( 0 );
                return result;
            }
        }
        
        throw new NoSuchElementException( "No more elements" );
    }
    
    /**
     *  Add another object to the enumeration.
     **/
    public void add( Object add ) {
        if( closed )
            throw new IllegalStateException( "Enumeration was closed" );
        
        synchronized( sequence ) {
            sequence.add( add );
            sequence.notify();
        }
    }
    
    /**
     *  There will be no more objects added.
     **/
    public void close() {
        closed = true;
        synchronized( sequence ) {
            sequence.notify();
        }
    }
}