Class EmptySequence
- All Implemented Interfaces:
GroundedValue
,Sequence
- Since:
- 9.5. Generified in 9.9. Generification reverted in 11.0.
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Method Summary
Modifier and TypeMethodDescriptionboolean
Get the effective boolean value - always falseboolean
Is this expression the same as another expression?static EmptySequence
Get the implicit instance of this classfinal int
Get the length of the sequenceGet the string value of this sequence, as an instance ofString
.Get the string value of this sequence, as an instance ofUnicodeString
.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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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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getUnicodeStringValue
Description copied from interface:GroundedValue
Get the string value of this sequence, as an instance ofUnicodeString
. The string value of an item is the result of applying the XPath 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 separatorThe result of this method is always equivalent to the result of the
GroundedValue.getStringValue()
method. Use this method in preference either (a) if you need to use the value in a context where aUnicodeString
is required, or (b) if the underlying value is held as aUnicodeString
, or in a form that is readily converted to aUnicodeString
. This is typically the case (i) when the value is a text or element node in a TinyTree, and (ii) when the value is aStringItem
: that is, an atomic value of typexs:string
.- Specified by:
getUnicodeStringValue
in interfaceGroundedValue
- Returns:
- the string value of the sequence.
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getStringValue
Description copied from interface:GroundedValue
Get the string value of this sequence, as an instance ofString
. The string value of an item is the result of applying the XPath 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.The result of this method is always equivalent to the result of the
GroundedValue.getUnicodeStringValue()
method. Use this method in preference either (a) if you need to use the value in a context where aString
is required, or (b) if the underlying value is held as aString
, or in a form that is readily converted to aString
. This is typically the case (i) when the value is an attribute node in a TinyTree, or (ii) any kind of node in a third-party tree model such as DOM.- Specified by:
getStringValue
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 empty iterator
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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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