Package net.sf.saxon.expr

Class TailIterator

java.lang.Object
net.sf.saxon.expr.TailIterator
All Implemented Interfaces:
Closeable, AutoCloseable, LastPositionFinder, SequenceIterator, LookaheadIterator
public class TailIterator extends Object implements SequenceIterator, LastPositionFinder, LookaheadIterator
TailIterator iterates over a base sequence starting at an element other than the first. The base sequence is represented by an iterator which is consumed in the process

  • Method Details

    • make

      public static SequenceIterator make(SequenceIterator base, int start) throws XPathException
      Static factory method. Creates a TailIterator, unless the base Iterator is an ArrayIterator, in which case it optimizes by creating a new ArrayIterator directly over the underlying array. This optimization is important when doing recursion over a node-set using repeated calls of $nodes[position()>1]
      Parameters:
      base - An iteration of the items to be filtered. The state of this iterator after the operation is undefined - it may or may not be consumed
      start - The position of the first item to be included (origin 1). If <= 1, the whole of the base sequence is returned
      Returns:
      an iterator over the items in the sequence from the start item to the end of the sequence. The returned iterator will not necessarily be an instance of this class.
      Throws:
      XPathException - if a dynamic error occurs

    • next

      public Item next()
      Description copied from interface: SequenceIterator
      Get the next item in the sequence. This method changes the state of the iterator.
      Specified by:
      next in interface SequenceIterator
      Returns:
      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.

    • 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
      Returns:
      true if there are more items in the sequence

    • 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
      Returns:
      the number of items in the sequence

    • 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.

      For example, the iterator returned by the unparsed-text-lines() function has a close() method that causes the underlying input stream to be closed, whether or not the file has been read to completion.

      Closing an iterator is important 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.

      Closing an iterator is not necessary if the iterator is read to completion: if a call on SequenceIterator.next() returns null, the iterator will be closed automatically. An explicit call on SequenceIterator.close() is needed only when iteration is abandoned prematurely.

      It is not possible to guarantee that an iterator that is not read to completion or will be closed. For example, if a lazy-evaluated variable $var is passed to a user-written function, the function may access $var[1] only; we have no way of knowing whether further items will be read. For this reason, any SequenceIterator that holds resources which need to be closed should use the Cleaner mechanism. The Configuration holds a Cleaner, and resources held by a SequenceIterator should be registered with the Cleaner; if the SequenceIterator is then garbage-collected without being closed, the Cleaner will ensure that the underlying resources are closed. (An example of a SequenceIterator that uses this mechanism is the UnparsedTextIterator).

      Specified by:
      close in interface AutoCloseable
      Specified by:
      close in interface Closeable
      Specified by:
      close in interface SequenceIterator