Package net.sf.saxon.value
Class EmptySequence<T extends Item>
java.lang.Object
net.sf.saxon.value.EmptySequence<T>
- All Implemented Interfaces:
GroundedValue
,Sequence
An EmptySequence object represents a sequence containing no members.
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Field Summary
Fields -
Method Summary
Modifier and TypeMethodDescriptionasItem()
Return the value in the form of an Itemboolean
Get the effective boolean value - always falseboolean
Is this expression the same as another expression?static <T extends Item>
EmptySequence<T>Get the implicit instance of this classfinal int
Get the length of the sequenceGet the string value of this sequence.Get the string value of this sequence.int
hashCode()
head()
Get the first item in the sequence.itemAt
(int n) Get the n'th item in the sequence (starting from 0).iterate()
Return an iteration over the sequencereduce()
Reduce the sequence to its simplest form.subsequence
(int min, int length) Get a subsequence of the valuetoString()
Returns a string representation of the object.Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
Methods inherited from interface net.sf.saxon.om.GroundedValue
asIterable, concatenate, containsNode, materialize, toShortString
Methods inherited from interface net.sf.saxon.om.Sequence
makeRepeatable
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Field Details
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a
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Method Details
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getInstance
Get the implicit instance of this class- Returns:
- the singular instances of this class: an empty sequence
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getStringValue
Description copied from interface:GroundedValue
Get the string value of this sequence. The string value of an item is the result of applying the string() function. The string value of a sequence is the space-separated result of applying the string-join() function using a single space as the separator- Specified by:
getStringValue
in interfaceGroundedValue
- Returns:
- the string value of the sequence.
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getStringValueCS
Description copied from interface:GroundedValue
Get the string value of this sequence. The string value of an item is the result of applying the string() function. The string value of a sequence is the space-separated result of applying the string-join() function using a single space as the separator- Specified by:
getStringValueCS
in interfaceGroundedValue
- Returns:
- the string value of the sequence.
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head
Get the first item in the sequence.- Specified by:
head
in interfaceGroundedValue
- Specified by:
head
in interfaceSequence
- Returns:
- the first item in the sequence if there is one, or null if the sequence is empty
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iterate
Return an iteration over the sequence- Specified by:
iterate
in interfaceGroundedValue
- Specified by:
iterate
in interfaceSequence
- Returns:
- an iterator (meaning a Saxon
SequenceIterator
rather than a JavaIterator
) over all the items in this Sequence.
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asItem
Return the value in the form of an Item- Returns:
- the value in the form of an Item
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getLength
public final int getLength()Get the length of the sequence- Specified by:
getLength
in interfaceGroundedValue
- Returns:
- always 0 for an empty sequence
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equals
Is this expression the same as another expression?- Overrides:
equals
in classObject
- Throws:
ClassCastException
- if the values are not comparable
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hashCode
public int hashCode() -
effectiveBooleanValue
public boolean effectiveBooleanValue()Get the effective boolean value - always false- Specified by:
effectiveBooleanValue
in interfaceGroundedValue
- Returns:
- the effective boolean value
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itemAt
Get the n'th item in the sequence (starting from 0). This is defined for all Values, but its real benefits come for a sequence Value stored extensionally (or for a MemoClosure, once all the values have been read)- Specified by:
itemAt
in interfaceGroundedValue
- Parameters:
n
- position of the required item, counting from zero.- Returns:
- the n'th item in the sequence, where the first item in the sequence is numbered zero. If n is negative or >= the length of the sequence, returns null.
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subsequence
Get a subsequence of the value- Specified by:
subsequence
in interfaceGroundedValue
- Parameters:
min
- the index of the first item to be included in the result, counting from zero. A negative value is taken as zero. If the value is beyond the end of the sequence, an empty sequence is returnedlength
- the number of items to be included in the result. Specify Integer.MAX_VALUE to get the subsequence up to the end of the base sequence. If the value is negative, an empty sequence is returned. If the value goes off the end of the sequence, the result returns items up to the end of the sequence- Returns:
- the required subsequence. If min is
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toString
Returns a string representation of the object. -
reduce
Reduce the sequence to its simplest form. If the value is an empty sequence, the result will be EmptySequence.getInstance(). If the value is a single atomic value, the result will be an instance of AtomicValue. If the value is a single item of any other kind, the result will be an instance of SingletonItem. Otherwise, the result will typically be unchanged.- Specified by:
reduce
in interfaceGroundedValue
- Returns:
- the simplified sequence
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