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The source code
package org.apache.lucene.search;
/**
* Copyright 2004 The Apache Software Foundation
*
* Licensed 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.IndexReader;
import org.apache.lucene.index.Term;
import org.apache.lucene.index.TermEnum;
/** Abstract class for enumerating a subset of all terms.
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() 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 (term != null && 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;
}
}
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