it.unimi.di.mg4j.search
Class FalseDocumentIterator

java.lang.Object
  it.unimi.di.mg4j.search.AbstractDocumentIterator
      it.unimi.di.mg4j.search.FalseDocumentIterator

All Implemented Interfaces:

DocumentIterator

public class FalseDocumentIterator
extends AbstractDocumentIterator

An empty document iterator.

Field Summary

Fields inherited from class it.unimi.di.mg4j.search.AbstractDocumentIterator

curr, weight

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

END_OF_LIST

Constructor Summary

protected

FalseDocumentIterator(Index index)

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.
void	dispose() Disposes this document iterator, releasing all resources.
static FalseDocumentIterator	getInstance(Index index) Creates a false document iterator with given index.
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.
int	nextDocument() Returns the next document provided by this document iterator, or DocumentIterator.END_OF_LIST if no more documents are available.
int	skipTo(int n) Skips all documents smaller than n.

Methods inherited from class it.unimi.di.mg4j.search.AbstractDocumentIterator

document, ensureOnADocument, mayHaveNext, weight, weight

Methods inherited from class java.lang.Object

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

Constructor Detail

FalseDocumentIterator

protected FalseDocumentIterator(Index index)

Method Detail

getInstance

public static FalseDocumentIterator getInstance(Index index)

Creates a false document iterator with given index.

Parameters:

index - the index of this iterator.

Returns:

a false document iterator with given index.

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.

Returns:

an interval iterator.

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.

Parameters:

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

Returns:

an interval iterator over the current document in 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).

Returns:

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

See Also:

DocumentIterator.intervalIterator(Index)

indices

public ReferenceSet<Index> indices()

Description copied from interface: DocumentIterator

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

Returns:

the set of indices over which this iterator is built.

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.

Returns:

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

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().

Parameters:

n - a document pointer.

Returns:

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

accept

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

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.

Parameters:

visitor - the visitor.

Returns:

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

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.

Parameters:

visitor - the visitor.

Returns:

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

See Also:

DocumentIterator.accept(DocumentIteratorVisitor), CounterCollectionVisitor

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.