filteriterator.java

Java的面向对象数据库系统的源代码

/*
 * Copyright 2001 (C) MetaStuff, Ltd. All Rights Reserved.
 * 
 * This software is open source. 
 * See the bottom of this file for the licence.
 * 
 * $Id: FilterIterator.java,v 1.5 2002/10/17 11:53:21 maartenc Exp $
 */

package org.dom4j.tree;

import java.util.Iterator;
import java.util.NoSuchElementException;

/** <p><code>FilterIterator</code> is an abstract base class which is useful
  * for implementors of {@link Iterator} which filter an existing iterator.
  *
  * @author <a href="mailto:[e-mail]">James Strachan</a>
  * @version $Revision: 1.5 $
  */
public abstract class FilterIterator implements Iterator {
    
    protected Iterator proxy;
    private Object next;
    private boolean first = true;
    
    public FilterIterator(Iterator proxy) {
        this.proxy = proxy;
    }


    public boolean hasNext() {
        if ( first ) {
            next = findNext();
            first = false;
        }
        return next != null;
    }

    public Object next() throws NoSuchElementException {
        if ( ! hasNext() ) {
            throw new NoSuchElementException();
        }
        Object answer = this.next;
        this.next = findNext();
        return answer;
    }

    /**
     * Always throws UnsupportedOperationException as this class 
     * does look-ahead with its internal iterator.
     *
     * @throws UnsupportedOperationException  always
     */
    public void remove() {
        throw new UnsupportedOperationException();
    }
    
    /** Filter method to perform some matching on the given element.
      * 
      * @return true if the given element matches the filter
      * and should be appear in the iteration
      */
    protected abstract boolean matches(Object element);
    
    
    protected Object findNext() {
        if ( proxy != null ) {
            while (proxy.hasNext()) {
                Object next = proxy.next();
                if ( next != null &&  matches(next) ) {
                    return next;
                }
            }
            proxy = null;
        }
        return null;
    }
}




/*
 * Redistribution and use of this software and associated documentation
 * ("Software"), with or without modification, are permitted provided
 * that the following conditions are met:
 *
 * 1. Redistributions of source code must retain copyright
 *    statements and notices.  Redistributions must also contain a
 *    copy of this document.
 *
 * 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 name "DOM4J" must not be used to endorse or promote
 *    products derived from this Software without prior written
 *    permission of MetaStuff, Ltd.  For written permission,
 *    please contact [e-mail].
 *
 * 4. Products derived from this Software may not be called "DOM4J"
 *    nor may "DOM4J" appear in their names without prior written
 *    permission of MetaStuff, Ltd. DOM4J is a registered
 *    trademark of MetaStuff, Ltd.
 *
 * 5. Due credit should be given to the DOM4J Project
 *    (http://dom4j.org/).
 *
 * THIS SOFTWARE IS PROVIDED BY METASTUFF, LTD. AND CONTRIBUTORS
 * ``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
 * METASTUFF, LTD. 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.
 *
 * Copyright 2001 (C) MetaStuff, Ltd. All Rights Reserved.
 *
 * $Id: FilterIterator.java,v 1.5 2002/10/17 11:53:21 maartenc Exp $
 */