Class Value<T extends Item>
- java.lang.Object
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- net.sf.saxon.value.Value<T>
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- All Implemented Interfaces:
ValueRepresentation<T>
- Direct Known Subclasses:
AtomicValue
,Closure
,EmptySequence
,IntegerRange
,SequenceExtent
,ShareableSequence
,SingletonItem
public abstract class Value<T extends Item> extends java.lang.Object implements ValueRepresentation<T>
A value is the result of an expression but it is also an expression in its own right. Note that every value can be regarded as a sequence - in many cases, a sequence of length one.
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Field Summary
Fields Modifier and Type Field Description static int
INDETERMINATE_ORDERING
Constant returned by compareTo() method to indicate an indeterminate ordering between two values-
Fields inherited from interface net.sf.saxon.om.ValueRepresentation
EMPTY_VALUE_ARRAY
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Constructor Summary
Constructors Constructor Description Value()
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Method Summary
All Methods Static Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description Item
asItem()
Return the value in the form of an Itemstatic Item
asItem(ValueRepresentation value)
Static method to make an Item from a Valuestatic <T extends Item>
SequenceIterator<T>asIterator(ValueRepresentation<T> val)
Static method to get an Iterator over any ValueRepresentation (which may be either a Value or a NodeInfo or a FunctionItemstatic <T extends Item>
Value<T>asValue(ValueRepresentation<T> val)
Static method to make a Value from a given Item (which may be either an AtomicValue or a NodeInfo or a FunctionItemvoid
checkPermittedContents(SchemaType parentType, StaticContext env, boolean whole)
Check statically that the results of the expression are capable of constructing the content of a given schema type.static java.lang.Object
convertToJava(Item item)
Convert an XPath value to a Java object.boolean
effectiveBooleanValue()
Get the effective boolean value of the expression.boolean
equals(java.lang.Object obj)
Compare two (sequence) values for equality.static Value
fromItem(Item item)
Static method to get a Value from an Itemjava.lang.CharSequence
getCanonicalLexicalRepresentation()
Get the canonical lexical representation as defined in XML Schema.int
getCardinality()
Determine the cardinalityItemType
getItemType(TypeHierarchy th)
Determine the data type of the items in the expression, if possiblestatic SequenceIterator
getIterator(ValueRepresentation val)
Get a SequenceIterator over a ValueRepresentationint
getLength()
Get the length of the sequencejava.lang.Comparable
getSchemaComparable()
Get a Comparable value that implements the XML Schema ordering comparison semantics for this value.static int
getSequenceLength(ValueRepresentation val)
Static method to get the length of a ValueRepresentation (the number of items in the sequence)java.lang.String
getStringValue()
Convert the value to a string, using the serialization rules.java.lang.CharSequence
getStringValueCS()
Get the value of the item as a CharSequence.int
hashCode()
boolean
isIdentical(Value v)
Determine whether two values are identical, as determined by XML Schema rules.T
itemAt(int n)
Get the n'th item in the sequence (starting from 0).abstract SequenceIterator<T>
iterate()
Iterate over the items contained in this value.void
process(XPathContext context)
Process the value as an instruction, without returning any tail callsValue
reduce()
Reduce a value to its simplest form.
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Field Detail
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INDETERMINATE_ORDERING
public static final int INDETERMINATE_ORDERING
Constant returned by compareTo() method to indicate an indeterminate ordering between two values- See Also:
- Constant Field Values
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Method Detail
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asValue
public static <T extends Item> Value<T> asValue(ValueRepresentation<T> val)
Static method to make a Value from a given Item (which may be either an AtomicValue or a NodeInfo or a FunctionItem- Parameters:
val
- The supplied value, or null, indicating the empty sequence.- Returns:
- The supplied value, if it is a value, or a SingletonNode that wraps the item, if it is a node. If the supplied value was null, return an EmptySequence
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getSequenceLength
public static int getSequenceLength(ValueRepresentation val) throws XPathException
Static method to get the length of a ValueRepresentation (the number of items in the sequence)- Parameters:
val
- The supplied value, or null, indicating the empty sequence.- Returns:
- The length of the supplied value, considered as a sequence
- Throws:
XPathException
- if an error occurs (for example, if the supplied value is a Closure and needs to be evaluated to determine the length of the result)
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asItem
public static Item asItem(ValueRepresentation value) throws XPathException
Static method to make an Item from a Value- Parameters:
value
- the value to be converted- Returns:
- null if the value is an empty sequence; or the only item in the value if it is a singleton sequence
- Throws:
XPathException
- if the Value contains multiple items
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asItem
public Item asItem() throws XPathException
Return the value in the form of an Item- Returns:
- the value in the form of an Item
- Throws:
XPathException
- if an error occurs, notably if this value is a sequence containing more than one item
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fromItem
public static Value fromItem(Item item)
Static method to get a Value from an Item- Parameters:
item
- the supplied item- Returns:
- the item expressed as a Value
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asIterator
public static <T extends Item> SequenceIterator<T> asIterator(ValueRepresentation<T> val) throws XPathException
Static method to get an Iterator over any ValueRepresentation (which may be either a Value or a NodeInfo or a FunctionItem- Parameters:
val
- The supplied value, or null, indicating the empty sequence.- Returns:
- The supplied value, if it is a value, or a SingletonNode that wraps the item, if it is a node. If the supplied value was null, return an EmptySequence
- Throws:
XPathException
- if an error occurs
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getIterator
public static SequenceIterator getIterator(ValueRepresentation val) throws XPathException
Get a SequenceIterator over a ValueRepresentation- Parameters:
val
- the value to iterate over- Returns:
- the iterator
- Throws:
XPathException
- if an error occurs (typically when the value is a Closure that needs to be evaluated)
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iterate
public abstract SequenceIterator<T> iterate() throws XPathException
Iterate over the items contained in this value.- Returns:
- an iterator over the sequence of items
- Throws:
XPathException
- if a dynamic error occurs. This is possible only in the case of values that are materialized lazily, that is, where the iterate() method leads to computation of an expression that delivers the values.
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getStringValueCS
public java.lang.CharSequence getStringValueCS() throws XPathException
Get the value of the item as a CharSequence. This is in some cases more efficient than the version of the method that returns a String.- Specified by:
getStringValueCS
in interfaceValueRepresentation<T extends Item>
- Returns:
- the result of converting the value to a string
- Throws:
XPathException
- The method can fail if evaluation of the value has been deferred, and if a failure occurs during the deferred evaluation. It can also occur for values such as function items and maps that have no string value. No failure is possible in the case of an AtomicValue or a Node.
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getCanonicalLexicalRepresentation
public java.lang.CharSequence getCanonicalLexicalRepresentation()
Get the canonical lexical representation as defined in XML Schema. This is not always the same as the result of casting to a string according to the XPath rules.- Returns:
- the canonical lexical representation if defined in XML Schema; otherwise, the result of casting to string according to the XPath 2.0 rules
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getItemType
public ItemType getItemType(TypeHierarchy th)
Determine the data type of the items in the expression, if possible- Parameters:
th
- The TypeHierarchy. If null is supplied, the resulting item type may be less precise.- Returns:
- for the default implementation: AnyItemType (not known)
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getCardinality
public int getCardinality()
Determine the cardinality- Returns:
- the cardinality
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itemAt
public T itemAt(int n) throws XPathException
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)- 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.
- Throws:
XPathException
- if an error occurs (for example if the value is a Closure that needs to be evaluated to find the Nth item)
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getLength
public int getLength() throws XPathException
Get the length of the sequence- Returns:
- the number of items in the sequence
- Throws:
XPathException
- if an error occurs (for example if the value is a closure that needs to be read to determine its length)
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process
public void process(XPathContext context) throws XPathException
Process the value as an instruction, without returning any tail calls- Parameters:
context
- The dynamic context, giving access to the current node, the current variables, etc.- Throws:
XPathException
- if an error occurs (for example if the value is a closure that needs to be evaluated)
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getStringValue
public java.lang.String getStringValue() throws XPathException
Convert the value to a string, using the serialization rules. For atomic values this is the same as a cast; for sequence values it gives a space-separated list.- Specified by:
getStringValue
in interfaceValueRepresentation<T extends Item>
- Returns:
- the result of converting the value to a string
- Throws:
XPathException
- The method can fail if evaluation of the value has been deferred, and if a failure occurs during the deferred evaluation. No failure is possible in the case of an AtomicValue.
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effectiveBooleanValue
public boolean effectiveBooleanValue() throws XPathException
Get the effective boolean value of the expression. This returns false if the value is the empty sequence, a zero-length string, a number equal to zero, or the boolean false. Otherwise it returns true.- Returns:
- the effective boolean value
- Throws:
XPathException
- if any dynamic error occurs evaluating the expression
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getSchemaComparable
public java.lang.Comparable getSchemaComparable()
Get a Comparable value that implements the XML Schema ordering comparison semantics for this value. The default implementation is written to compare sequences of atomic values. This method is overridden for AtomicValue and its subclasses.In the case of data types that are partially ordered, the returned Comparable extends the standard semantics of the compareTo() method by returning the value
INDETERMINATE_ORDERING
when there is no defined order relationship between two given values.- Returns:
- a Comparable that follows XML Schema comparison rules
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equals
public boolean equals(java.lang.Object obj)
Compare two (sequence) values for equality. This method throws an UnsupportedOperationException, because it should not be used: there are too many "equality" operators that can be defined on values for the concept to be meaningful.Consider creating an XPathComparable from each value, and comparing those; or creating a SchemaComparable to achieve equality comparison as defined in XML Schema.
- Overrides:
equals
in classjava.lang.Object
- Throws:
java.lang.UnsupportedOperationException
- (always)
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hashCode
public int hashCode()
- Overrides:
hashCode
in classjava.lang.Object
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isIdentical
public boolean isIdentical(Value v)
Determine whether two values are identical, as determined by XML Schema rules. This is a stronger test than equality (even schema-equality); for example two dateTime values are not identical unless they are in the same timezone.Note that even this check ignores the type annotation of the value. The integer 3 and the short 3 are considered identical, even though they are not fully interchangeable. "Identical" means the same point in the value space, regardless of type annotation.
Although the schema rules cover atomic values only, this method also handles values that include nodes, using node identity in this case.
The empty sequence is considered identical to the empty sequence.
NaN is identical to itself.
Function items are not identical to anything except themselves
- Parameters:
v
- the other value to be compared with this one- Returns:
- true if the two values are identical, false otherwise.
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checkPermittedContents
public void checkPermittedContents(SchemaType parentType, StaticContext env, boolean whole) throws XPathException
Check statically that the results of the expression are capable of constructing the content of a given schema type.- Parameters:
parentType
- The schema typeenv
- the static contextwhole
- true if this value accounts for the entire content of the containing node- Throws:
XPathException
- if the expression doesn't match the required content type
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reduce
public Value reduce() throws XPathException
Reduce a value to its simplest form. If the value is a closure or some other form of deferred value such as a FunctionCallPackage, then it is reduced to a SequenceExtent. If it is a SequenceExtent containing a single item, then it is reduced to that item. One consequence that is exploited by class FilterExpression is that if the value is a singleton numeric value, then the result will be an instance of NumericValue- Returns:
- the value in simplified form
- Throws:
XPathException
- if an error occurs
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convertToJava
public static java.lang.Object convertToJava(Item item) throws XPathException
Convert an XPath value to a Java object. An atomic value is returned as an instance of the best available Java class. If the item is a node, the node is "unwrapped", to return the underlying node in the original model (which might be, for example, a DOM or JDOM node).- Parameters:
item
- the item to be converted- Returns:
- the value after conversion
- Throws:
XPathException
- if an error occurs: for example, if the XPath value is an integer and is too big to fit in a Java long
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