net.sf.saxon.expr
Class MappingIterator

java.lang.Object
  |
  +--net.sf.saxon.expr.MappingIterator
All Implemented Interfaces:
SequenceIterator

public final class MappingIterator
extends java.lang.Object
implements SequenceIterator

MappingIterator merges a sequence of sequences into a single flat sequence. It takes as inputs an iteration, and a mapping function to be applied to each Item returned by that iteration. The mapping function itself returns another iteration. The result is an iteration of the concatenation of all the iterations returned by the mapping function.

This is a powerful class. It is used, with different mapping functions, in a great variety of ways. It underpins the way that "for" expressions and path expressions are evaluated, as well as sequence expressions. It is also used in the implementation of the document(), key(), and id() functions.


Constructor Summary
MappingIterator(SequenceIterator base, MappingFunction action, XPathContext context, java.lang.Object info)
          Construct a MappingIterator that will apply a specified MappingFunction to each Item returned by the base iterator.
 
Method Summary
 Item current()
          Get the current value in the sequence (the one returned by the most recent call on next()).
 SequenceIterator getAnother()
          Get another SequenceIterator that iterates over the same items as the original, but which is repositioned at the start of the sequence.
 boolean hasNext()
          Determine whether there are more items to come.
 Item next()
          Get the next item in the sequence.
 int position()
          Get the current position.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

MappingIterator

public MappingIterator(SequenceIterator base,
                       MappingFunction action,
                       XPathContext context,
                       java.lang.Object info)
                throws XPathException
Construct a MappingIterator that will apply a specified MappingFunction to each Item returned by the base iterator.

Parameters:
base - the base iterator
action - the mapping function to be applied
context - the processing context. This should be supplied only if each item to be processed is to become the context item. In this case "base" should be the same as context.getCurrentIterator().
info - an arbitrary object to be passed as a parameter to the mapping function each time it is called
Method Detail

hasNext

public boolean hasNext()
                throws XPathException
Description copied from interface: SequenceIterator
Determine whether there are more items to come.
This method must be called before next() is called to get the next item, and next() must not be called unless hasNext() returns true. The hasNext() method must not change the current position, it must be possible to call hasNext() repeatedly and get the same result each time.

Specified by:
hasNext in interface SequenceIterator
Returns:
true if there are more items available
Throws:
XPathException - if any error occurs while determining whether there are more items in the sequence

next

public Item next()
          throws XPathException
Description copied from interface: SequenceIterator
Get the next item in the sequence.
This must not be called unless hasNext() has been called to test whether there is a next item.

Specified by:
next in interface SequenceIterator
Returns:
the next item
Throws:
XPathException - if an error occurs retrieving the next item

current

public Item current()
Description copied from interface: SequenceIterator
Get the current value in the sequence (the one returned by the most recent call on next()). This will be null before the first call of next().

Specified by:
current in interface SequenceIterator
Returns:
the current item, the one most recently returned by a call on next(); or null, if next() has not been called

position

public int position()
Description copied from interface: SequenceIterator
Get the current position. This will be zero before the first call on next(), otherwise it will be the number of times that next() has been called.

Specified by:
position in interface SequenceIterator
Returns:
the current position, the position of the item returned by the most recent call of next()

getAnother

public SequenceIterator getAnother()
                            throws XPathException
Description copied from interface: SequenceIterator
Get another SequenceIterator that iterates over the same items as the original, but which is repositioned at the start of the sequence.

Specified by:
getAnother in interface SequenceIterator
Returns:
a SequenceIterator that iterates over the same items, positioned before the first item
Throws:
XPathException - if any error occurs