it.unimi.di.mg4j.index
Class Index.EmptyIndexIterator

java.lang.Object
  it.unimi.di.mg4j.index.Index.EmptyIndexIterator

All Implemented Interfaces:

IndexIterator, DocumentIterator, Serializable

Enclosing class:

Index

public class Index.EmptyIndexIterator
extends Object
implements IndexIterator, Serializable

An iterator returning no documents based on this index.

Note that accept(DocumentIteratorVisitor) does nothing and returns true, whereas acceptOnTruePaths(DocumentIteratorVisitor) throws an IllegalStateException, weight() returns 1 and weight(double) is a no-op.

See Also:

Serialized Form

Field Summary

int	id
String	term
int	termNumber
double	weight

Fields inherited from interface it.unimi.di.mg4j.index.IndexIterator

END_OF_POSITIONS

Fields inherited from interface it.unimi.di.mg4j.search.DocumentIterator

END_OF_LIST

Constructor Summary

Index.EmptyIndexIterator()

Method Summary

<T> T	accept(DocumentIteratorVisitor<T> visitor) Accepts a visitor.
<T> T	acceptOnTruePaths(DocumentIteratorVisitor<T> visitor) Accepts a visitor after a call to DocumentIterator.nextDocument(), limiting recursion to true paths.
int	count() Returns the count, that is, the number of occurrences of the term in the current document.
void	dispose() Disposes this document iterator, releasing all resources.
int	document() Returns the last document returned by DocumentIterator.nextDocument().
int	frequency() Returns the frequency, that is, the number of documents that will be returned by this iterator.
int	id() Returns the id of this index iterator.
IndexIterator	id(int id) Sets the id of this index iterator.
Index	index() Returns the index over which this iterator is built.
ReferenceSet<Index>	indices() Returns the set of indices over which this iterator is built.
IntervalIterator	intervalIterator() Returns the interval iterator of this document iterator for single-index queries.
IntervalIterator	intervalIterator(Index index) Returns the interval iterator of this document iterator for the given index.
Reference2ReferenceMap<Index,IntervalIterator>	intervalIterators() Returns an unmodifiable map from indices to interval iterators.
boolean	mayHaveNext() Returns whether there may be a next document, possibly with false positives.
int	nextDocument() Returns the next document provided by this document iterator, or DocumentIterator.END_OF_LIST if no more documents are available.
int	nextPosition() Returns the next position at which the term appears in the current document.
Payload	payload() Returns the payload, if any, associated with the current document.
int	skipTo(int n) Skips all documents smaller than n.
String	term() Returns the term whose inverted list is returned by this index iterator.
Index.EmptyIndexIterator	term(CharSequence term) Sets the term whose inverted list is returned by this index iterator.
int	termNumber() Returns the number of the term whose inverted list is returned by this index iterator.
IndexIterator	termNumber(int termNumber)
double	weight() Returns the weight associated with this iterator.
IndexIterator	weight(double weight) Returns the weight of this index iterator.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

term

public String term

weight

public double weight

id

public int id

termNumber

public int termNumber

Constructor Detail

Index.EmptyIndexIterator

public Index.EmptyIndexIterator()

Method Detail

document

public int document()

Description copied from interface: DocumentIterator

Returns the last document returned by DocumentIterator.nextDocument().

Specified by:

document in interface DocumentIterator

Returns:

the last document returned by DocumentIterator.nextDocument(), -1 if no document has been returned yet, and DocumentIterator.END_OF_LIST if the list of results has been exhausted.

indices

public ReferenceSet<Index> indices()

Description copied from interface: DocumentIterator

Returns the set of indices over which this iterator is built.

Specified by:

indices in interface DocumentIterator

Returns:

the set of indices over which this iterator is built.

intervalIterator

public IntervalIterator intervalIterator()

Description copied from interface: DocumentIterator

Returns the interval iterator of this document iterator for single-index queries.

This is a commodity method that can be used only for queries built over a single index.

Specified by:

intervalIterator in interface DocumentIterator

Returns:

an interval iterator.

See Also:

DocumentIterator.intervalIterator(Index)

intervalIterators

public Reference2ReferenceMap<Index,IntervalIterator> intervalIterators()

Description copied from interface: DocumentIterator

Returns an unmodifiable map from indices to interval iterators.

After a call to DocumentIterator.nextDocument(), this map can be used to retrieve the intervals in the current document. An invocation of Map.get(java.lang.Object) on this map with argument index yields the same result as intervalIterator(index).

Specified by:

intervalIterators in interface DocumentIterator

Returns:

a map from indices to interval iterators over the current document.

See Also:

DocumentIterator.intervalIterator(Index)

intervalIterator

public IntervalIterator intervalIterator(Index index)

Description copied from interface: DocumentIterator

Returns the interval iterator of this document iterator for the given index.

After a call to DocumentIterator.nextDocument(), this iterator can be used to retrieve the intervals in the current document (the one returned by DocumentIterator.nextDocument()) for the index index.

Note that if all indices have positions, it is guaranteed that at least one index will return an interval. However, for disjunctive queries it cannot be guaranteed that all indices will return an interval.

Indices without positions always return IntervalIterators.TRUE. Thus, in presence of indices without positions it is possible that no intervals at all are available.

Specified by:

intervalIterator in interface DocumentIterator

Parameters:

index - an index (must be one over which the query was built).

Returns:

an interval iterator over the current document in index.

nextDocument

public int nextDocument()

Description copied from interface: DocumentIterator

Returns the next document provided by this document iterator, or DocumentIterator.END_OF_LIST if no more documents are available.

Specified by:

nextDocument in interface DocumentIterator

Returns:

the next document, or DocumentIterator.END_OF_LIST if no more documents are available.

mayHaveNext

public boolean mayHaveNext()

Description copied from interface: DocumentIterator

Returns whether there may be a next document, possibly with false positives.

Specified by:

mayHaveNext in interface DocumentIterator

Returns:

true there may be a next document; false if certainly there is no next document.

skipTo

public int skipTo(int n)

Description copied from interface: DocumentIterator

Skips all documents smaller than n.

Define the current document k associated with this document iterator as follows:

• -1, if DocumentIterator.nextDocument() and this method have never been called;
• DocumentIterator.END_OF_LIST, if a call to this method or to DocumentIterator.nextDocument() returned DocumentIterator.END_OF_LIST;
• the last value returned by a call to DocumentIterator.nextDocument() or this method, otherwise.

If k is larger than or equal to n, then this method does nothing and returns k. Otherwise, a call to this method is equivalent to

 while( ( k = nextDocument() ) < n );
 return k;
 

Thus, when a result k ≠ DocumentIterator.END_OF_LIST is returned, the state of this iterator will be exactly the same as after a call to DocumentIterator.nextDocument() that returned k. In particular, the first document larger than or equal to n (when returned by this method) will not be returned by the next call to DocumentIterator.nextDocument().

Specified by:

skipTo in interface DocumentIterator

Parameters:

n - a document pointer.

Returns:

a document pointer larger than or equal to n if available, DocumentIterator.END_OF_LIST otherwise.

frequency

public int frequency()

Description copied from interface: IndexIterator

Returns the frequency, that is, the number of documents that will be returned by this iterator.

Specified by:

frequency in interface IndexIterator

Returns:

the number of documents that will be returned by this iterator.

payload

public Payload payload()

Description copied from interface: IndexIterator

Returns the payload, if any, associated with the current document.

Specified by:

payload in interface IndexIterator

Returns:

the payload associated with the current document.

count

public int count()

Description copied from interface: IndexIterator

Returns the count, that is, the number of occurrences of the term in the current document.

Specified by:

count in interface IndexIterator

Returns:

the count (number of occurrences) of the term in the current document.

dispose

public void dispose()

Description copied from interface: DocumentIterator

Disposes this document iterator, releasing all resources.

This method should propagate down to the underlying index iterators, where it should release resources such as open files and network connections. If you're doing your own resource tracking and pooling, then you do not need to call this method.

Specified by:

dispose in interface DocumentIterator

index

public Index index()

Description copied from interface: IndexIterator

Returns the index over which this iterator is built.

Specified by:

index in interface IndexIterator

Returns:

the index over which this iterator is built.

accept

public <T> T accept(DocumentIteratorVisitor<T> visitor)
         throws IOException

Description copied from interface: DocumentIterator

Accepts a visitor.

A document iterator is usually structured as composite, with operators as internal nodes and IndexIterators as leaves. This method implements the visitor pattern.

Specified by:

accept in interface DocumentIterator

Parameters:

visitor - the visitor.

Returns:

an object resulting from the visit, or null if the visit was interrupted.

Throws:

IOException

acceptOnTruePaths

public <T> T acceptOnTruePaths(DocumentIteratorVisitor<T> visitor)

Description copied from interface: DocumentIterator

Accepts a visitor after a call to DocumentIterator.nextDocument(), limiting recursion to true paths.

After a call to DocumentIterator.nextDocument(), a document iterator is positioned over a document. This call is equivalent to DocumentIterator.accept(DocumentIteratorVisitor), but visits only along true paths.

We define a true path as a path from the root of the composite that passes only through nodes whose associated subtree is positioned on the same document of the root. Note that OrDocumentIterators detach exhausted iterators from the composite tree, so true paths define the subtree that is causing the current document to satisfy the query represented by this document iterator.

For more elaboration, and the main application of this method, see CounterCollectionVisitor.

Specified by:

acceptOnTruePaths in interface DocumentIterator

Parameters:

visitor - the visitor.

Returns:

an object resulting from the visit, or null if the visit was interrupted.

See Also:

DocumentIterator.accept(DocumentIteratorVisitor), CounterCollectionVisitor

term

public String term()

Description copied from interface: IndexIterator

Returns the term whose inverted list is returned by this index iterator.

Usually, the term is automatically set by IndexReader.documents(CharSequence) or IndexReader.documents(int), but you can supply your own term with IndexIterator.term(CharSequence).

Specified by:

term in interface IndexIterator

Returns:

the term over which this iterator is built, as a compact mutable string.

See Also:

IndexIterator.termNumber()

term

public Index.EmptyIndexIterator term(CharSequence term)

Description copied from interface: IndexIterator

Sets the term whose inverted list is returned by this index iterator.

Usually, the term is automatically set by Index.documents(CharSequence) or by IndexReader.documents(CharSequence), but you can use this method to ensure that IndexIterator.term() doesn't throw an exception.

Specified by:

term in interface IndexIterator

Parameters:

term - a character sequence (that will be defensively copied) that will be assumed to be the term whose inverted list is returned by this index iterator.

Returns:

this index iterator.

id

public int id()

Description copied from interface: IndexIterator

Returns the id of this index iterator.

Specified by:

id in interface IndexIterator

Returns:

the id of this index iterator.

See Also:

IndexIterator.id(int)

id

public IndexIterator id(int id)

Description copied from interface: IndexIterator

Sets the id of this index iterator.

The id is an integer associated with each index iterator. It has no specific semantics, and can be used differently in different contexts. A typical usage pattern, for instance, is using it to assign a unique number to the index iterators contained in a composite document iterator (say, numbering consecutively the leaves of the composite).

Specified by:

id in interface IndexIterator

Parameters:

id - the new id for this index iterator.

Returns:

this index iterator.

termNumber

public int termNumber()

Description copied from interface: IndexIterator

Returns the number of the term whose inverted list is returned by this index iterator.

Usually, the term number is automatically set by IndexReader.documents(CharSequence) or IndexReader.documents(int).

Specified by:

termNumber in interface IndexIterator

Returns:

the number of the term over which this iterator is built.

See Also:

IndexIterator.term()

termNumber

public IndexIterator termNumber(int termNumber)

weight

public double weight()

Description copied from interface: DocumentIterator

Returns the weight associated with this iterator.

The number returned by this method has no fixed semantics: different scorers might choose different interpretations, or even ignore it.

Specified by:

weight in interface DocumentIterator

Returns:

the weight associated with this iterator.

weight

public IndexIterator weight(double weight)

Description copied from interface: IndexIterator

Returns the weight of this index iterator.

Specified by:

weight in interface IndexIterator

Specified by:

weight in interface DocumentIterator

Parameters:

weight - the weight of this index iterator.

Returns:

this document iterator.

See Also:

DocumentIterator.weight(double)

nextPosition

public int nextPosition()
                 throws IOException

Description copied from interface: IndexIterator

Returns the next position at which the term appears in the current document.

Specified by:

nextPosition in interface IndexIterator

Returns:

the next position of the current document in which the current term appears, or IndexIterator.END_OF_POSITIONS if there are no more positions.

Throws:

IOException