filteredtermenum.java

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package org.apache.lucene.search;

/* ====================================================================
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2001 The Apache Software Foundation.  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
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Apache" and "Apache Software Foundation" and
 *    "Apache Lucene" must not be used to endorse or promote products
 *    derived from this software without prior written permission. For
 *    written permission, please contact [e-mail].
 *
 * 5. Products derived from this software may not be called "Apache",
 *    "Apache Lucene", nor may "Apache" appear in their name, without
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 *
 * 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
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 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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 * 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 the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */

import java.io.IOException;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;
import org.apache.lucene.index.TermEnum;

/** Abstract class for enumerating a subset of all terms. 

  <p>Term enumerations are always ordered by Term.compareTo().  Each term in
  the enumeration is greater than all that precede it.  */
public abstract class FilteredTermEnum extends TermEnum {
    private Term currentTerm = null;
    private TermEnum actualEnum = null;
    
    public FilteredTermEnum(IndexReader reader, Term term) throws IOException {}

    /** Equality compare on the term */
    protected abstract boolean termCompare(Term term);
    
    /** Equality measure on the term */
    protected abstract float difference();

    /** Indiciates the end of the enumeration has been reached */
    protected abstract boolean endEnum();
    
    protected void setEnum(TermEnum actualEnum) throws IOException {
        this.actualEnum = actualEnum;
        // Find the first term that matches
        Term term = actualEnum.term();
        if (termCompare(term)) 
            currentTerm = term;
        else next();
    }
    
    /** 
     * Returns the docFreq of the current Term in the enumeration.
     * Initially invalid, valid after next() called for the first time. 
     */
    public int docFreq() {
        if (actualEnum == null) return -1;
        return actualEnum.docFreq();
    }
    
    /** Increments the enumeration to the next element.  True if one exists. */
    public boolean next() throws IOException {
        if (actualEnum == null) return false; // the actual enumerator is not initialized!
        currentTerm = null;
        while (currentTerm == null) {
            if (endEnum()) return false;
            if (actualEnum.next()) {
                Term term = actualEnum.term();
                if (termCompare(term)) {
                    currentTerm = term;
                    return true;
                }
            }
            else return false;
        }
        currentTerm = null;
        return false;
    }
    
    /** Returns the current Term in the enumeration.
     * Initially invalid, valid after next() called for the first time. */
    public Term term() {
        return currentTerm;
    }
    
    /** Closes the enumeration to further activity, freeing resources.  */
    public void close() throws IOException {
        actualEnum.close();
        currentTerm = null;
        actualEnum = null;
    }
}