Package com.saxonica.functions.qt4

Class DuplicateValues.DuplicatesIterator

  • All Implemented Interfaces:
    java.io.Closeable, java.lang.AutoCloseable, SequenceIterator
    Enclosing class:
    DuplicateValues
    public static class DuplicateValues.DuplicatesIterator
extends java.lang.Object
implements SequenceIterator
    Iterator class to return the distinct values in a sequence

    • Constructor Detail

      • DuplicatesIterator

        public DuplicatesIterator​(SequenceIterator base,
                          StringCollator collator,
                          XPathContext context)
        Create an iterator over the distinct values in a sequence
        Parameters:
        base - the input sequence. This must return atomic values only.
        collator - The comparer used to obtain comparison keys from each value; these comparison keys are themselves compared using equals().
        context - the XPath dynamic context

    • Method Detail

      • next

        public AtomicValue next()
        Get the next item in the sequence.
        Specified by:
        next in interface SequenceIterator
        Returns:
        the next item, or null if there are no more items.

      • 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 java.lang.AutoCloseable
        Specified by:
        close in interface java.io.Closeable
        Specified by:
        close in interface SequenceIterator