Package org.apache.lucene.search

Class Sort

java.lang.Object

org.apache.lucene.search.Sort

public class Sort
extends java.lang.Object

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

Field Summary

Fields

Modifier and Type	Field	Description
static Sort	INDEXORDER	Represents sorting by index order.
static Sort	RELEVANCE	Represents sorting by computed relevance.

Constructor Summary

Constructors

Constructor	Description
Sort()	Sorts by computed relevance.
Sort(SortField field)	Sorts by the criteria in the given SortField.
Sort(SortField... fields)	Sorts in succession by the criteria in each SortField.

Method Summary

Modifier and Type	Method	Description
boolean	equals(java.lang.Object o)	Returns true if o is equal to this.
SortField[]	getSort()	Representation of the sort criteria.
int	hashCode()	Returns a hash code value for this object.
Sort	rewrite(IndexSearcher searcher)	Rewrites the SortFields in this Sort, returning a new Sort if any of the fields changes during their rewriting.
void	setSort(SortField field)	Sets the sort to the given criteria.
void	setSort(SortField... fields)	Sets the sort to the given criteria in succession.
java.lang.String	toString()

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Field Detail

RELEVANCE

public static final Sort RELEVANCE

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.

INDEXORDER

public static final Sort INDEXORDER

Represents sorting by index order.

Constructor Detail

Sort

public Sort()

Sorts by computed relevance. This is the same sort criteria as calling IndexSearcher#search()without a sort criteria, only with slightly more overhead.

Sort

public Sort(SortField field)

Sorts by the criteria in the given SortField.

Sort

public Sort(SortField... fields)

Sorts in succession by the criteria in each SortField.

Method Detail

setSort

public void setSort(SortField field)

Sets the sort to the given criteria.

setSort

public void setSort(SortField... fields)

Sets the sort to the given criteria in succession.

getSort

public SortField[] getSort()

Representation of the sort criteria.

Returns:

Array of SortField objects used in this sort criteria

rewrite

public Sort rewrite(IndexSearcher searcher)
             throws java.io.IOException

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

Parameters:

searcher - IndexSearcher to use in the rewriting

Returns:

this if the Sort/Fields have not changed, or a new Sort if there is a change

Throws:

java.io.IOException - Can be thrown by the rewriting

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object

equals

public boolean equals(java.lang.Object o)

Returns true if o is equal to this.

Overrides:

equals in class java.lang.Object

hashCode

public int hashCode()

Returns a hash code value for this object.

Overrides:

hashCode in class java.lang.Object