Class ItemCheckingIterator
- All Implemented Interfaces:
Closeable
,AutoCloseable
,LastPositionFinder
,SequenceIterator
,LookaheadIterator
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Constructor Summary
ConstructorsConstructorDescriptionItemCheckingIterator
(SequenceIterator base, Consumer<Item> action) Construct an ItemCheckingIterator that will apply a specified Function to each Item returned by the base iterator. -
Method Summary
Modifier and TypeMethodDescriptionvoid
close()
Close the iterator.int
Get the last position (that is, the number of items in the sequence).boolean
hasNext()
Determine whether there are more items to come.next()
Get the next item in the sequence.boolean
Ask whether this iterator supports use of theLastPositionFinder.getLength()
method.boolean
Ask whether the hasNext() method can be called.
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Constructor Details
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ItemCheckingIterator
Construct an ItemCheckingIterator that will apply a specified Function to each Item returned by the base iterator.- Parameters:
base
- the base iteratoraction
- the mapping function to be applied.
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Method Details
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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 interfaceLookaheadIterator
- Returns:
- true if the
LookaheadIterator.hasNext()
method is available
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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 interfaceLookaheadIterator
- Returns:
- true if there are more items in the sequence
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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 interfaceSequenceIterator
- 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.
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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 onSequenceIterator.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, anySequenceIterator
that holds resources which need to be closed should use theCleaner
mechanism. TheConfiguration
holds aCleaner
, and resources held by aSequenceIterator
should be registered with theCleaner
; if theSequenceIterator
is then garbage-collected without being closed, theCleaner
will ensure that the underlying resources are closed. (An example of aSequenceIterator
that uses this mechanism is theUnparsedTextIterator
).- Specified by:
close
in interfaceAutoCloseable
- Specified by:
close
in interfaceCloseable
- Specified by:
close
in interfaceSequenceIterator
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supportsGetLength
public boolean supportsGetLength()Description copied from interface:LastPositionFinder
Ask whether this iterator supports use of theLastPositionFinder.getLength()
method. This method should always be called before callingLastPositionFinder.getLength()
, because an iterator that implements this interface may support use ofLastPositionFinder.getLength()
in some situations and not in others- Specified by:
supportsGetLength
in interfaceLastPositionFinder
- Returns:
- true if the
LastPositionFinder.getLength()
method can be called to determine the length of the underlying sequence.
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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 theLastPositionFinder.supportsGetLength()
has been called and has returned true.- Specified by:
getLength
in interfaceLastPositionFinder
- Returns:
- the number of items in the sequence
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