Package net.sf.saxon.expr

Class DescendingRangeIterator

java.lang.Object

net.sf.saxon.expr.RangeIterator

net.sf.saxon.expr.DescendingRangeIterator

All Implemented Interfaces:

java.io.Closeable, java.lang.AutoCloseable, LastPositionFinder, SequenceIterator, AtomicIterator, GroundedIterator, LookaheadIterator, ReversibleIterator

public class DescendingRangeIterator
extends net.sf.saxon.expr.RangeIterator
implements AtomicIterator, ReversibleIterator, LastPositionFinder, LookaheadIterator

Iterator that produces numeric values in a monotonic sequence, ascending or descending. Although a range expression (N to M) is always in ascending order, applying the reverse() function will produce a RangeIterator that works in descending order.

Constructor Summary

Constructors

Constructor	Description
DescendingRangeIterator(long start, long step, long end)	Create an iterator over a range of integers in monotonic descending order

Method Summary

Modifier and Type	Method	Description
IntegerValue	getFirst()
IntegerValue	getLast()
int	getLength()	Get the last position (that is, the number of items in the sequence).
IntegerValue	getMax()
IntegerValue	getMin()
GroundedValue	getResidue()	Return a GroundedValue containing all the remaining items in the sequence returned by this SequenceIterator, starting at the current position.
AtomicIterator	getReverseIterator()	Get a new SequenceIterator that returns the same items in reverse order.
IntegerValue	getStep()	Get the increment between successive values.
boolean	hasNext()	Determine whether there are more items to come.
boolean	isActuallyGrounded()	Ask if the iterator is actually grounded.
GroundedValue	materialize()	Return a GroundedValue containing all the items in the sequence returned by this SequenceIterator.
IntegerValue	next()	Get the next atomic value in the sequence.
boolean	supportsGetLength()	Ask whether this iterator supports use of the LastPositionFinder.getLength() method.
boolean	supportsHasNext()	Ask whether the hasNext() method can be called.

Methods inherited from class net.sf.saxon.expr.RangeIterator

getProperties, makeRangeIterator

Methods inherited from class java.lang.Object

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

Methods inherited from interface net.sf.saxon.om.SequenceIterator

close

Constructor Detail

DescendingRangeIterator

public DescendingRangeIterator(long start,
                               long step,
                               long end)

Create an iterator over a range of integers in monotonic descending order

Parameters:

start - the first integer to be delivered (the highest in the range)

step - the difference between successive values, supplied as a positive integer

end - the last integer to be delivered (the lowest in the range). Must be <= start

Method Detail

isActuallyGrounded

public boolean isActuallyGrounded()

Description copied from interface: GroundedIterator

Ask if the iterator is actually grounded. This method must be called before calling GroundedIterator.materialize() or GroundedIterator.getResidue(), because the iterator might be grounded under some conditions and not others (usually when it delegates to another iterator)

Specified by:

isActuallyGrounded in interface GroundedIterator

Returns:

true if this iterator is grounded

materialize

public GroundedValue materialize()

Return a GroundedValue containing all the items in the sequence returned by this SequenceIterator. This should be an "in-memory" value, not a Closure. This method does not change the state of the iterator (in particular, it does not consume the iterator).

Specified by:

materialize in interface GroundedIterator

Overrides:

materialize in class net.sf.saxon.expr.RangeIterator

Returns:

the corresponding Value

Throws:

UncheckedXPathException - in the cases of subclasses (such as the iterator over a MemoClosure) which cause evaluation of expressions while materializing the value.

getResidue

public GroundedValue getResidue()

Return a GroundedValue containing all the remaining items in the sequence returned by this SequenceIterator, starting at the current position. This should be an "in-memory" value, not a Closure. This method does not change the state of the iterator (in particular, it does not consume the iterator).

Specified by:

getResidue in interface GroundedIterator

Overrides:

getResidue in class net.sf.saxon.expr.RangeIterator

Returns:

the corresponding Value

Throws:

UncheckedXPathException - in the cases of subclasses (such as the iterator over a MemoClosure) which cause evaluation of expressions while materializing the value.

getFirst

public IntegerValue getFirst()

getLast

public IntegerValue getLast()

getMin

public IntegerValue getMin()

getMax

public IntegerValue getMax()

getStep

public IntegerValue getStep()

Get the increment between successive values. For a descending iterator this will be negatiive value.

Returns:

the increment between successive values

supportsHasNext

public boolean supportsHasNext()

Description copied from interface: LookaheadIterator

Ask 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)

Specified by:

supportsHasNext in interface LookaheadIterator

Returns:

true if the LookaheadIterator.hasNext() method is available

hasNext

public boolean hasNext()

Description copied from interface: LookaheadIterator

Determine 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 LookaheadIterator.supportsHasNext() is true.

Specified by:

hasNext in interface LookaheadIterator

Overrides:

hasNext in class net.sf.saxon.expr.RangeIterator

Returns:

true if there are more items in the sequence

next

public IntegerValue next()

Description copied from interface: AtomicIterator

Get the next atomic value in the sequence.

Specified by:

next in interface AtomicIterator

Specified by:

next in interface SequenceIterator

Overrides:

next in class net.sf.saxon.expr.RangeIterator

Returns:

the next Item. If there are no more items, return null.

supportsGetLength

public boolean supportsGetLength()

Description copied from interface: LastPositionFinder

Ask 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

Specified by:

supportsGetLength in interface LastPositionFinder

Returns:

true if the LastPositionFinder.getLength() method can be called to determine the length of the underlying sequence.

getLength

public int getLength()

Description copied from interface: LastPositionFinder

Get the last position (that is, the number of items in the sequence). This method is non-destructive: it does not change the state of the iterator. The result is undefined if the next() method of the iterator has already returned null. This method must not be called unless the LastPositionFinder.supportsGetLength() has been called and has returned true.

Specified by:

getLength in interface LastPositionFinder

Overrides:

getLength in class net.sf.saxon.expr.RangeIterator

Returns:

the number of items in the sequence

getReverseIterator

public AtomicIterator getReverseIterator()

Description copied from interface: ReversibleIterator

Get a new SequenceIterator that returns the same items in reverse order. If this SequenceIterator is an AxisIterator, then the returned SequenceIterator must also be an AxisIterator.

Specified by:

getReverseIterator in interface ReversibleIterator

Returns:

an iterator over the items in reverse order