- All Implemented Interfaces:
public class GroupByIterator extends java.lang.Object implements GroupIterator, LastPositionFinder, LookaheadIteratorA GroupByIterator iterates over a sequence of groups defined by xsl:for-each-group group-by="x". The groups are returned in order of first appearance. Note that an item can appear in several groups; indeed, an item may be the leading item of more than one group, which means that knowing the leading item is not enough to know the current group.
The GroupByIterator acts as a SequenceIterator, where successive calls of next() return the leading item of each group in turn. The current item of the iterator is therefore the leading item of the current group. To get access to all the members of the current group, the method iterateCurrentGroup() is used; this underpins the current-group() function in XSLT. The grouping key for the current group is available via the getCurrentGroupingKey() method.
Nested Class Summary
Nested Classes Modifier and Type Class Description
All Methods Instance Methods Concrete Methods Modifier and Type Method Description
getCurrentGroup()Get the contents of the current group as a java List
getCurrentGroupingKey()Get the value of the grouping key for the current group
getLength()Get the last position (that is, the number of groups)
getSnapShot(XPathContext context)Get a sequence which is a snapshot of this sequence at the current position
hasNext()Determine whether there are more items to come.
iterateCurrentGroup()Get an iterator over the items in the current group
next()Get the next item in the sequence.
supportsGetLength()Ask whether this iterator supports use of the
supportsHasNext()Ask whether the hasNext() method can be called.
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
public GroupByIterator(SequenceIterator population, Expression keyExpression, XPathContext keyContext, StringCollator collator, boolean composite) throws XPathExceptionCreate a GroupByIterator
population- iterator over the population to be grouped
keyExpression- the expression used to calculate the grouping key
keyContext- dynamic context for calculating the grouping key
collator- Collation to be used for comparing grouping keys
composite- true if grouping keys are to be treated as composite keys
XPathException- if an error occurs
public AtomicSequence getCurrentGroupingKey()Get the value of the grouping key for the current group
public SequenceIterator iterateCurrentGroup()Get an iterator over the items in the current group
public java.util.List<Item> getCurrentGroup()Get the contents of the current group as a java List
- the contents of the current group
public boolean supportsHasNext()Description copied from interface:
LookaheadIteratorAsk whether the hasNext() method can be called. This method must be called before calling hasNext(), because some iterators implement this interface, but only support look-ahead under particular circumstances (this is usually because they delegate to another iterator)
public boolean hasNext()Description copied from interface:
LookaheadIteratorDetermine whether there are more items to come. Note that this operation is stateless and it is not necessary (or usual) to call it before calling next(). It is used only when there is an explicit need to tell if we are at the last element.
This method must not be called unless the result of
public Item next()Description copied from interface:
SequenceIteratorGet the next item in the sequence. This method changes the state of the iterator.
- Specified by:
- the next item, or null if there are no more items. Once a call on next() has returned null, no further calls should be made. The preferred action for an iterator if subsequent calls on next() are made is to return null again, and all implementations within Saxon follow this rule.
public boolean supportsGetLength()Description copied from interface:
LastPositionFinderAsk whether this iterator supports use of the
LastPositionFinder.getLength()method. This method should always be called before calling
LastPositionFinder.getLength(), because an iterator that implements this interface may support use of
LastPositionFinder.getLength()in some situations and not in others
public int getLength()Get the last position (that is, the number of groups)
public ManualGroupIterator getSnapShot(XPathContext context)Description copied from interface:
GroupIteratorGet a sequence which is a snapshot of this sequence at the current position