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.Serializable;
/**
* Encapsulates sort criteria for returned hits.
*
* <p>The fields used to determine sort order must be carefully chosen.
* Documents must contain a single term in such a field,
* and the value of the term should indicate the document's relative position in
* a given sort order. The field must be indexed, but should not be tokenized,
* and does not need to be stored (unless you happen to want it back with the
* rest of your document data). In other words:
*
* <dl><dd><code>document.add (new Field ("byNumber", Integer.toString(x), false, true, false));</code>
* </dd></dl>
*
* <p><h3>Valid Types of Values</h3>
*
* <p>There are three possible kinds of term values which may be put into
* sorting fields: Integers, Floats, or Strings. Unless
* {@link SortField SortField} objects are specified, the type of value
* in the field is determined by parsing the first term in the field.
*
* <p>Integer term values should contain only digits and an optional
* preceeding negative sign. Values must be base 10 and in the range
* <code>Integer.MIN_VALUE</code> and <code>Integer.MAX_VALUE</code> inclusive.
* Documents which should appear first in the sort
* should have low value integers, later documents high values
* (i.e. the documents should be numbered <code>1..n</code> where
* <code>1</code> is the first and <code>n</code> the last).
*
* <p>Float term values should conform to values accepted by
* {@link Float Float.valueOf(String)} (except that <code>NaN</code>
* and <code>Infinity</code> are not supported).
* Documents which should appear first in the sort
* should have low values, later documents high values.
*
* <p>String term values can contain any valid String, but should
* not be tokenized. The values are sorted according to their
* {@link Comparable natural order}. Note that using this type
* of term value has higher memory requirements than the other
* two types.
*
* <p><h3>Object Reuse</h3>
*
* <p>One of these objects can be
* used multiple times and the sort order changed between usages.
*
* <p>This class is thread safe.
*
* <p><h3>Memory Usage</h3>
*
* <p>Sorting uses of caches of term values maintained by the
* internal HitQueue(s). The cache is static and contains an integer
* or float array of length <code>IndexReader.maxDoc()</code> for each field
* name for which a sort is performed. In other words, the size of the
* cache in bytes is:
*
* <p><code>4 * IndexReader.maxDoc() * (# of different fields actually used to sort)</code>
*
* <p>For String fields, the cache is larger: in addition to the
* above array, the value of every term in the field is kept in memory.
* If there are many unique terms in the field, this could
* be quite large.
*
* <p>Note that the size of the cache is not affected by how many
* fields are in the index and <i>might</i> be used to sort - only by
* the ones actually used to sort a result set.
*
* <p>The cache is cleared each time a new <code>IndexReader</code> is
* passed in, or if the value returned by <code>maxDoc()</code>
* changes for the current IndexReader. This class is not set up to
* be able to efficiently sort hits from more than one index
* simultaneously.
*
* <p>Created: Feb 12, 2004 10:53:57 AM
*
* @author Tim Jones (Nacimiento Software)
* @since lucene 1.4
* @version $Id: Sort.java,v 1.7 2004/04/05 17:23:38 ehatcher Exp $
*/
public class Sort
implements Serializable {
/** Represents sorting by computed relevance. Using this sort criteria
* returns the same results as calling {@link Searcher#search(Query) Searcher#search()}
* without a sort criteria, only with slightly more overhead. */
public static final Sort RELEVANCE = new Sort();
/** Represents sorting by index order. */
public static final Sort INDEXORDER = new Sort (SortField.FIELD_DOC);
// internal representation of the sort criteria
SortField[] fields;
/** Sorts by computed relevance. This is the same sort criteria as
* calling {@link Searcher#search(Query) Searcher#search()} without a sort criteria, only with
* slightly more overhead. */
public Sort() {
this (new SortField[]{SortField.FIELD_SCORE, SortField.FIELD_DOC});
}
/** Sorts by the terms in <code>field</code> then by index order (document
* number). The type of value in <code>field</code> is determined
* automatically.
* @see SortField#AUTO
*/
public Sort (String field) {
setSort (field, false);
}
/** Sorts possibly in reverse by the terms in <code>field</code> then by
* index order (document number). The type of value in <code>field</code> is determined
* automatically.
* @see SortField#AUTO
*/
public Sort (String field, boolean reverse) {
setSort (field, reverse);
}
/** Sorts in succession by the terms in each field.
* The type of value in <code>field</code> is determined
* automatically.
* @see SortField#AUTO
*/
public Sort (String[] fields) {
setSort (fields);
}
/** Sorts by the criteria in the given SortField. */
public Sort (SortField field) {
setSort (field);
}
/** Sorts in succession by the criteria in each SortField. */
public Sort (SortField[] fields) {
setSort (fields);
}
/** Sets the sort to the terms in <code>field</code> then by index order
* (document number). */
public final void setSort (String field) {
setSort (field, false);
}
/** Sets the sort to the terms in <code>field</code> possibly in reverse,
* then by index order (document number). */
public void setSort (String field, boolean reverse) {
SortField[] nfields = new SortField[]{
new SortField (field, SortField.AUTO, reverse),
SortField.FIELD_DOC
};
fields = nfields;
}
/** Sets the sort to the terms in each field in succession. */
public void setSort (String[] fieldnames) {
final int n = fieldnames.length;
SortField[] nfields = new SortField[n];
for (int i = 0; i < n; ++i) {
nfields[i] = new SortField (fieldnames[i], SortField.AUTO);
}
fields = nfields;
}
/** Sets the sort to the given criteria. */
public void setSort (SortField field) {
this.fields = new SortField[]{field};
}
/** Sets the sort to the given criteria in succession. */
public void setSort (SortField[] fields) {
this.fields = fields;
}
public String toString() {
StringBuffer buffer = new StringBuffer();
for (int i = 0; i < fields.length; i++) {
buffer.append(fields[i].toString());
if ((i +1) < fields.length)
buffer.append(',');
}
return buffer.toString();
}
}
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