net.sf.saxon.tree.iter

Class EmptyIterator

java.lang.Object

net.sf.saxon.tree.iter.EmptyIterator

All Implemented Interfaces:

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

public class EmptyIterator
extends java.lang.Object
implements SequenceIterator, ReversibleIterator, LastPositionFinder, GroundedIterator, LookaheadIterator, AtomizedValueIterator

EmptyIterator: an iterator over an empty sequence. Since such an iterator has no state, only one instance is required; therefore a singleton instance is available via the static getInstance() method.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	EmptyIterator() Protected constructor

Method Summary

Modifier and Type	Method and Description
static EmptyIterator	emptyIterator()
static EmptyIterator	getInstance() Get an EmptyIterator, an iterator over an empty sequence.
int	getLength() Get the position of the last item in the sequence.
GroundedValue	getResidue() Return a GroundedValue containing all the remaining items in the sequence returned by this SequenceIterator, starting at the current position.
EmptyIterator	getReverseIterator() Get another iterator over the same items, in reverse order.
boolean	hasNext() Determine whether there are more items to come.
boolean	isActuallyGrounded() Ask if the iterator is actually grounded.
GroundedValue	materialize() Return a Value containing all the items in the sequence returned by this SequenceIterator.
Item	next() Get the next item.
AtomicSequence	nextAtomizedValue() Deliver the atomic value that is next in the atomized result
static AtomicIterator	ofAtomic() Static method to get an empty AtomicIterator
static AxisIterator	ofNodes() Static method to get an empty AxisIterator
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 java.lang.Object

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

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

close, discharge

Constructor Detail

EmptyIterator

protected EmptyIterator()

Protected constructor

Method Detail

getInstance

public static EmptyIterator getInstance()

Get an EmptyIterator, an iterator over an empty sequence.

Returns:

an EmptyIterator (in practice, this always returns the same one)

emptyIterator

public static EmptyIterator emptyIterator()

nextAtomizedValue

public AtomicSequence nextAtomizedValue()

Deliver the atomic value that is next in the atomized result

Specified by:

nextAtomizedValue in interface AtomizedValueIterator

Returns:

the next atomic value

next

public Item next()

Get the next item.

Specified by:

next in interface SequenceIterator

Returns:

the next item. For the EmptyIterator this is always 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()

Get the position of the last item in the sequence.

Specified by:

getLength in interface LastPositionFinder

Returns:

the position of the last item in the sequence, always zero in this implementation

getReverseIterator

public EmptyIterator getReverseIterator()

Get another iterator over the same items, in reverse order.

Specified by:

getReverseIterator in interface ReversibleIterator

Returns:

a reverse iterator over an empty sequence (in practice, it returns the same iterator each time)

materialize

public GroundedValue materialize()

Return a Value containing all the items in the sequence returned by this SequenceIterator. This should be an "in-memory" value, not a Closure.

Specified by:

materialize in interface GroundedIterator

Returns:

the corresponding Value

getResidue

public GroundedValue getResidue()

Description copied from interface: GroundedIterator

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

Returns:

the corresponding Value

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()

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.

Specified by:

hasNext in interface LookaheadIterator

Returns:

true if there are more nodes

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

ofNodes

public static AxisIterator ofNodes()

Static method to get an empty AxisIterator

Returns:

an empty AxisIterator

ofAtomic

public static AtomicIterator ofAtomic()

Static method to get an empty AtomicIterator

Returns:

an empty AtomicIterator