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 org.apache.lucene.util.PriorityQueue;
final class HitQueue extends PriorityQueue<ScoreDoc> {
private boolean prePopulate;
/**
* Creates a new instance with <code>size</code> elements. If
* <code>prePopulate</code> is set to true, the queue will pre-populate itself
* with sentinel objects and set its {@link #size()} to <code>size</code>. In
* that case, you should not rely on {@link #size()} to get the number of
* actual elements that were added to the queue, but keep track yourself.<br>
* <b>NOTE:</b> in case <code>prePopulate</code> is true, you should pop
* elements from the queue using the following code example:
*
* <pre>
* PriorityQueue pq = new HitQueue(10, true); // pre-populate.
* ScoreDoc top = pq.top();
*
* // Add/Update one element.
* top.score = 1.0f;
* top.doc = 0;
* top = (ScoreDoc) pq.updateTop();
* int totalHits = 1;
*
* // Now pop only the elements that were *truly* inserted.
* // First, pop all the sentinel elements (there are pq.size() - totalHits).
* for (int i = pq.size() - totalHits; i > 0; i--) pq.pop();
*
* // Now pop the truly added elements.
* ScoreDoc[] results = new ScoreDoc[totalHits];
* for (int i = totalHits - 1; i >= 0; i--) {
* results[i] = (ScoreDoc) pq.pop();
* }
* </pre>
*
* <p><b>NOTE</b>: This class pre-allocate a full array of
* length <code>size</code>.
*
* @param size
* the requested size of this queue.
* @param prePopulate
* specifies whether to pre-populate the queue with sentinel values.
* @see #getSentinelObject()
*/
HitQueue(int size, boolean prePopulate) {
this.prePopulate = prePopulate;
initialize(size);
}
// Returns null if prePopulate is false.
@Override
protected ScoreDoc getSentinelObject() {
// Always set the doc Id to MAX_VALUE so that it won't be favored by
// lessThan. This generally should not happen since if score is not NEG_INF,
// TopScoreDocCollector will always add the object to the queue.
return !prePopulate ? null : new ScoreDoc(Integer.MAX_VALUE, Float.NEGATIVE_INFINITY);
}
@Override
protected final boolean lessThan(ScoreDoc hitA, ScoreDoc hitB) {
if (hitA.score == hitB.score)
return hitA.doc > hitB.doc;
else
return hitA.score < hitB.score;
}
}