Package net.sf.saxon.om

Class EmptyIterator

java.lang.Object
net.sf.saxon.om.EmptyIterator
All Implemented Interfaces:
LastPositionFinder, ReversibleIterator, AxisIterator, GroundedIterator, LookaheadIterator, SequenceIterator, UnfailingIterator
public class EmptyIterator extends Object implements AxisIterator, ReversibleIterator, LastPositionFinder, GroundedIterator, LookaheadIterator
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.

  • Method Details

    • 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)

    • moveNext

      public boolean moveNext()
      Move to the next node, without returning it. Returns true if there is a next node, false if the end of the sequence has been reached. After calling this method, the current node may be retrieved using the current() function.
      Specified by:
      moveNext in interface AxisIterator

    • next

      public Item next()
      Get the next item.
      Specified by:
      next in interface SequenceIterator
      Specified by:
      next in interface UnfailingIterator
      Returns:
      the next item. For the EmptyIterator this is always null.

    • current

      public Item current()
      Get the current item, that is, the item returned by the most recent call of next().
      Specified by:
      current in interface SequenceIterator
      Specified by:
      current in interface UnfailingIterator
      Returns:
      the current item. For the EmptyIterator this is always null.

    • position

      public int position()
      Get the position of the current item.
      Specified by:
      position in interface SequenceIterator
      Specified by:
      position in interface UnfailingIterator
      Returns:
      the position of the current item. For the EmptyIterator this is always zero (whether or not the next() method has been called).

    • getLastPosition

      public int getLastPosition()
      Get the position of the last item in the sequence.
      Specified by:
      getLastPosition in interface LastPositionFinder
      Returns:
      the position of the last item in the sequence, always zero in this implementation

    • close

      public void close()
      Description copied from interface: SequenceIterator
      Close the iterator. This indicates to the supplier of the data that the client does not require any more items to be delivered by the iterator. This may enable the supplier to release resources. After calling close(), no further calls on the iterator should be made; if further calls are made, the effect of such calls is undefined.

      (Currently, closing an iterator is important only when the data is being "pushed" in another thread. Closing the iterator terminates that thread and means that it needs to do no additional work. Indeed, failing to close the iterator may cause the push thread to hang waiting for the buffer to be emptied.)

      Specified by:
      close in interface SequenceIterator

    • iterateAxis

      public AxisIterator iterateAxis(byte axis, NodeTest test)
      Return an iterator over an axis, starting at the current node.
      Specified by:
      iterateAxis in interface AxisIterator
      Parameters:
      axis - the axis to iterate over, using a constant such as Axis.CHILD
      test - a predicate to apply to the nodes before returning them.
      Throws:
      NullPointerException - if there is no current node

    • atomize

      public Value atomize() throws XPathException
      Return the atomized value of the current node.
      Specified by:
      atomize in interface AxisIterator
      Returns:
      the atomized value.
      Throws:
      NullPointerException - if there is no current node
      XPathException

    • getStringValue

      public CharSequence getStringValue()
      Return the string value of the current node.
      Specified by:
      getStringValue in interface AxisIterator
      Returns:
      the string value, as an instance of CharSequence.
      Throws:
      NullPointerException - if there is no current node

    • getAnother

      public SequenceIterator getAnother()
      Get another iterator over the same items, positioned at the start.
      Specified by:
      getAnother in interface SequenceIterator
      Specified by:
      getAnother in interface UnfailingIterator
      Returns:
      another iterator over an empty sequence (in practice, it returns the same iterator each time)

    • getReverseIterator

      public SequenceIterator 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)

    • getProperties

      public int getProperties()
      Get properties of this iterator, as a bit-significant integer.
      Specified by:
      getProperties in interface SequenceIterator
      Returns:
      the properties of this iterator. This will be some combination of properties such as SequenceIterator.GROUNDED, SequenceIterator.LAST_POSITION_FINDER, and SequenceIterator.LOOKAHEAD. It is always acceptable to return the value zero, indicating that there are no known special properties. It is acceptable for the properties of the iterator to change depending on its state.

    • 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

    • 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