it.unimi.dsi.mg4j.search
Class DocumentIterators.EmptyDocumentIterator

java.lang.Object
  extended by it.unimi.dsi.fastutil.ints.AbstractIntIterator
      extended by it.unimi.dsi.mg4j.search.DocumentIterators.EmptyDocumentIterator
All Implemented Interfaces:
IntIterator, DocumentIterator, Iterable<Interval>, Iterator<Integer>
Enclosing class:
DocumentIterators

protected static class DocumentIterators.EmptyDocumentIterator
extends AbstractIntIterator
implements DocumentIterator

An empty document iterator with empty index set.


Constructor Summary
protected DocumentIterators.EmptyDocumentIterator()
           
 
Method Summary
 boolean accept(DocumentIteratorVisitor visitor)
          Accepts a visitor.
 boolean acceptOnTruePaths(DocumentIteratorVisitor visitor)
          Accepts a visitor after a call to DocumentIterator.nextDocument(), limiting recursion to true paths.
 void dispose()
          Disposes this document iterator, releasing all resources.
 int document()
          Returns the last document returned by DocumentIterator.nextDocument().
 boolean hasNext()
           
 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.
 IntervalIterator iterator()
          An alias for DocumentIterator.intervalIterator(), that has the same limitations (i.e., it will work only if there is just one index), and that catches IOExceptions.
 int nextDocument()
          Returns the next document provided by this document iterator, or -1 if no more documents are available.
 int nextInt()
          Returns the next document.
 int skipTo(int n)
          Skips all documents smaller than n.
 
Methods inherited from class it.unimi.dsi.fastutil.ints.AbstractIntIterator
next, remove, skip
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 
Methods inherited from interface it.unimi.dsi.fastutil.ints.IntIterator
skip
 
Methods inherited from interface java.util.Iterator
next, remove
 

Constructor Detail

DocumentIterators.EmptyDocumentIterator

protected DocumentIterators.EmptyDocumentIterator()
Method Detail

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)

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.

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)

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.

hasNext

public boolean hasNext()
Specified by:
hasNext in interface Iterator<Integer>

nextDocument

public int nextDocument()
Description copied from interface: DocumentIterator
Returns the next document provided by this document iterator, or -1 if no more documents are available.

Warning: the specification of this method has significantly changed as of MG4J 1.2. The special return value -1 is used to mark the end of iteration (a NoSuchElementException would have been thrown before in that case, so ho harm should be caused by this change). The reason for this change is providing fully lazy iteration over documents. Fully lazy iteration does not provide an hasNext() method—you have to actually ask for the next element and check the return value. Fully lazy iteration is much lighter on method calls (half) and in most (if not all) MG4J classes leads to a much simpler logic. Moreover, DocumentIterator.nextDocument() can be specified as throwing an IOException, which avoids the pernicious proliferation of try/catch blocks in very short, low-level methods (it was having a detectable impact on performance).

Specified by:
nextDocument in interface DocumentIterator
Returns:
the next document, or -1 if no more documents are available.

nextInt

public int nextInt()
Description copied from interface: DocumentIterator
Returns the next document.

Specified by:
nextInt in interface IntIterator
Specified by:
nextInt in interface DocumentIterator
Overrides:
nextInt in class AbstractIntIterator
See Also:
DocumentIterator.nextDocument()

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(), or -1 if no document has been returned yet.

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:

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 && k != -1 );
 return k == -1 ? Integer.MAX_VALUE : k;
 

Thus, when a result kInteger.MAX_VALUE 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, Integer.MAX_VALUE otherwise.

accept

public boolean accept(DocumentIteratorVisitor 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.

Specified by:
accept in interface DocumentIterator
Parameters:
visitor - the visitor.
Returns:
true if the visit should continue.

acceptOnTruePaths

public boolean acceptOnTruePaths(DocumentIteratorVisitor 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:
true if the visit should continue.
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.

Specified by:
dispose in interface DocumentIterator

iterator

public IntervalIterator iterator()
Description copied from interface: DocumentIterator
An alias for DocumentIterator.intervalIterator(), that has the same limitations (i.e., it will work only if there is just one index), and that catches IOExceptions.

Specified by:
iterator in interface DocumentIterator
Specified by:
iterator in interface Iterable<Interval>
Returns:
an interval iterator.