package org.apache.lucene.search;
/**
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import java.io.IOException;
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 {
/** the current term */
protected Term currentTerm = null;
/** the delegate enum - to set this member use {@link #setEnum} */
protected TermEnum actualEnum = null;
public FilteredTermEnum() {}
/** Equality compare on the term */
protected abstract boolean termCompare(Term term);
/** Equality measure on the term */
public abstract float difference();
/** Indicates the end of the enumeration has been reached */
protected abstract boolean endEnum();
/**
* use this method to set the actual TermEnum (e.g. in ctor),
* it will be automatically positioned on the first matching term.
*/
protected void setEnum(TermEnum actualEnum) throws IOException {
this.actualEnum = actualEnum;
// Find the first term that matches
Term term = actualEnum.term();
if (term != null && termCompare(term))
currentTerm = term;
else next();
}
/**
* Returns the docFreq of the current Term in the enumeration.
* Returns -1 if no Term matches or all terms have been enumerated.
*/
@Override
public int docFreq() {
if (currentTerm == null) return -1;
assert actualEnum != null;
return actualEnum.docFreq();
}
/** Increments the enumeration to the next element. True if one exists. */
@Override
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.
* Returns null if no Term matches or all terms have been enumerated. */
@Override
public Term term() {
return currentTerm;
}
/** Closes the enumeration to further activity, freeing resources. */
@Override
public void close() throws IOException {
if (actualEnum != null) actualEnum.close();
currentTerm = null;
actualEnum = null;
}
}