http://lucene.apache.org/lucene-parent/lucene-core: Apache Lucene Java Core (The Apache Software Foundation) 
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 * (the "License"); you may not use this file except in compliance with
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package org.apache.lucene.search;


import java.io.IOException;
import java.util.Arrays;



Encapsulates sort criteria for returned hits.

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:

document.add (new Field ("byNumber", Integer.toString(x), Field.Store.NO, Field.Index.NOT_ANALYZED));


Valid Types of Values


There are four possible kinds of term values which may be put into sorting fields: Integers, Longs, Floats, or Strings. Unless SortField objects are specified, the type of value in the field is determined by parsing the first term in the field. 
Integer term values should contain only digits and an optional
preceding negative sign.  Values must be base 10 and in the range
Integer.MIN_VALUE and Integer.MAX_VALUE 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 1..n where
1 is the first and n the last).

Long term values should contain only digits and an optional
preceding negative sign.  Values must be base 10 and in the range
Long.MIN_VALUE and Long.MAX_VALUE inclusive.
Documents which should appear first in the sort
should have low value integers, later documents high values.

Float term values should conform to values accepted by Float.valueOf(String) (except that NaN
and Infinity are not supported).
Documents which should appear first in the sort
should have low values, later documents high values.

String term values can contain any valid String, but should not be tokenized. The values are sorted according to their natural order. Note that using this type of term value has higher memory requirements than the other two types. 
Object Reuse


One of these objects can be
used multiple times and the sort order changed between usages.

This class is thread safe.

Memory Usage


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 IndexReader.maxDoc() for each field
name for which a sort is performed.  In other words, the size of the
cache in bytes is:

4 * IndexReader.maxDoc() * (# of different fields actually used to sort)

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.

Note that the size of the cache is not affected by how many
fields are in the index and might be used to sort - only by
the ones actually used to sort a result set.

Created: Feb 12, 2004 10:53:57 AM

Since:  lucene 1.4
/**
 * 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:
 *
 * <p><code>document.add (new Field ("byNumber", Integer.toString(x), Field.Store.NO, Field.Index.NOT_ANALYZED));</code></p>
 * 
 *
 * <h3>Valid Types of Values</h3>
 *
 * <p>There are four possible kinds of term values which may be put into
 * sorting fields: Integers, Longs, 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
 * preceding 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>Long term values should contain only digits and an optional
 * preceding negative sign.  Values must be base 10 and in the range
 * <code>Long.MIN_VALUE</code> and <code>Long.MAX_VALUE</code> inclusive.
 * Documents which should appear first in the sort
 * should have low value integers, later documents high values.
 * 
 * <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.
 *
 * <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.
 *
 * <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>Created: Feb 12, 2004 10:53:57 AM
 *
 * @since   lucene 1.4
 */
public class Sort {

  
Represents sorting by computed relevance. Using this sort criteria returns the same results as calling IndexSearcher#search()without a sort criteria, only with slightly more overhead. 
/**
   * Represents sorting by computed relevance. Using this sort criteria returns
   * the same results as calling
   * {@link IndexSearcher#search(Query,int) IndexSearcher#search()}without a sort criteria,
   * only with slightly more overhead.
   */
  public static final Sort RELEVANCE = new Sort();

  
Represents sorting by index order. 
/** 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 IndexSearcher#search()without a sort criteria, only with slightly more overhead. 
/**
   * Sorts by computed relevance. This is the same sort criteria as calling
   * {@link IndexSearcher#search(Query,int) IndexSearcher#search()}without a sort criteria,
   * only with slightly more overhead.
   */
  public Sort() {
    this(SortField.FIELD_SCORE);
  }

  
Sorts by the criteria in the given SortField. 
/** Sorts by the criteria in the given SortField. */
  public Sort(SortField field) {
    setSort(field);
  }

  
Sets the sort to the given criteria in succession: the
 first SortField is checked first, but if it produces a
 tie, then the second SortField is used to break the tie,
 etc.  Finally, if there is still a tie after all SortFields
 are checked, the internal Lucene docid is used to break it. 
/** Sets the sort to the given criteria in succession: the
   *  first SortField is checked first, but if it produces a
   *  tie, then the second SortField is used to break the tie,
   *  etc.  Finally, if there is still a tie after all SortFields
   *  are checked, the internal Lucene docid is used to break it. */
  public Sort(SortField... fields) {
    setSort(fields);
  }

  
Sets the sort to the given criteria. 
/** 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: the
 first SortField is checked first, but if it produces a
 tie, then the second SortField is used to break the tie,
 etc.  Finally, if there is still a tie after all SortFields
 are checked, the internal Lucene docid is used to break it. 
/** Sets the sort to the given criteria in succession: the
   *  first SortField is checked first, but if it produces a
   *  tie, then the second SortField is used to break the tie,
   *  etc.  Finally, if there is still a tie after all SortFields
   *  are checked, the internal Lucene docid is used to break it. */
  public void setSort(SortField... fields) {
    if (fields.length == 0) {
      throw new IllegalArgumentException("There must be at least 1 sort field");
    }
    this.fields = fields;
  }
  
  
Representation of the sort criteria.

Returns:Array of SortField objects used in this sort criteria
/**
   * Representation of the sort criteria.
   * @return Array of SortField objects used in this sort criteria
   */
  public SortField[] getSort() {
    return fields;
  }

  
Rewrites the SortFields in this Sort, returning a new Sort if any of the fields
changes during their rewriting.

Params:
  • searcher – IndexSearcher to use in the rewriting
Throws:
Returns:this if the Sort/Fields have not changed, or a new Sort if there is a change
@lucene.experimental
/**
   * Rewrites the SortFields in this Sort, returning a new Sort if any of the fields
   * changes during their rewriting.
   *
   * @param searcher IndexSearcher to use in the rewriting
   * @return {@code this} if the Sort/Fields have not changed, or a new Sort if there
   *        is a change
   * @throws IOException Can be thrown by the rewriting
   * @lucene.experimental
   */
  public Sort rewrite(IndexSearcher searcher) throws IOException {
    boolean changed = false;
    
    SortField[] rewrittenSortFields = new SortField[fields.length];
    for (int i = 0; i < fields.length; i++) {
      rewrittenSortFields[i] = fields[i].rewrite(searcher);
      if (fields[i] != rewrittenSortFields[i]) {
        changed = true;
      }
    }

    return (changed) ? new Sort(rewrittenSortFields) : this;
  }

  @Override
  public String toString() {
    StringBuilder buffer = new StringBuilder();

    for (int i = 0; i < fields.length; i++) {
      buffer.append(fields[i].toString());
      if ((i+1) < fields.length)
        buffer.append(',');
    }

    return buffer.toString();
  }

  
Returns true if o is equal to this. 
/** Returns true if <code>o</code> is equal to this. */
  @Override
  public boolean equals(Object o) {
    if (this == o) return true;
    if (!(o instanceof Sort)) return false;
    final Sort other = (Sort)o;
    return Arrays.equals(this.fields, other.fields);
  }

  
Returns a hash code value for this object. 
/** Returns a hash code value for this object. */
  @Override
  public int hashCode() {
    return 0x45aaf665 + Arrays.hashCode(fields);
  }

  
Returns true if the relevance score is needed to sort documents. 
/** Returns true if the relevance score is needed to sort documents. */
  public boolean needsScores() {
    for (SortField sortField : fields) {
      if (sortField.needsScores()) {
        return true;
      }
    }
    return false;
  }

}