Class Value

java.lang.Object
net.sf.saxon.value.Value
All Implemented Interfaces:
Serializable, SequenceIterable, ValueRepresentation
Direct Known Subclasses:
AtomicValue, Closure, EmptySequence, IntegerRange, SequenceExtent, ShareableSequence, SingletonNode

public abstract class Value extends Object implements Serializable, SequenceIterable, ValueRepresentation
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.
See Also:
  • Field Details

    • INDETERMINATE_ORDERING

      public static final int INDETERMINATE_ORDERING
      Constant returned by compareTo() method to indicate an indeterminate ordering between two values
      See Also:
    • EMPTY_CLASS_ARRAY

      public static final Class[] EMPTY_CLASS_ARRAY
  • Constructor Details

    • Value

      public Value()
  • Method Details

    • asValue

      public static Value asValue(ValueRepresentation val)
      Static method to make a Value from a given Item (which may be either an AtomicValue or a NodeInfo
      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
    • 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
    • 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
    • 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
    • asIterator

      public static SequenceIterator asIterator(ValueRepresentation val) throws XPathException
      Static method to get an Iterator over any ValueRepresentation (which may be either a Value or a NodeInfo
      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
    • stringToNumber

      public static double stringToNumber(CharSequence s) throws NumberFormatException
      Static method to convert strings to doubles.
      Parameters:
      s - the String to be converted
      Returns:
      a double representing the value of the String
      Throws:
      NumberFormatException - if the value cannot be converted
    • 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
    • iterate

      public abstract SequenceIterator 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.
    • iterate

      public final SequenceIterator iterate(XPathContext context) throws XPathException
      Return an iterator over the results of evaluating an expression
      Specified by:
      iterate in interface SequenceIterable
      Parameters:
      context - the dynamic evaluation context (not used in this implementation)
      Returns:
      an iterator over the items delivered by the expression
      Throws:
      XPathException
    • getStringValueCS

      public 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 interface ValueRepresentation
      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 or a Node.
    • getCanonicalLexicalRepresentation

      public 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
    • getItemType

      public ItemType getItemType(TypeHierarchy th)
      Determine the data type of the items in the expression, if possible
      Parameters:
      th - The TypeHierarchy. Can be null if the target is an AtomicValue.
      Returns:
      for the default implementation: AnyItemType (not known)
    • getCardinality

      public int getCardinality()
      Determine the cardinality
      Returns:
      the cardinality
    • itemAt

      public Item 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
    • getLength

      public int getLength() throws XPathException
      Get the length of the sequence
      Returns:
      the number of items in the sequence
      Throws:
      XPathException
    • 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
    • getStringValue

      public 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 interface ValueRepresentation
      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.
    • 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
    • getSchemaComparable

      public 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
    • equals

      public boolean equals(Object obj)
      Compare two (sequence) values for equality. This method implements the XPath eq operator, for cases where it is defined. For values containing nodes, nodes are compared for identity. In cases where eq is not defined, it throws ClassCastException. In cases where the result of eq is an empty sequence, this function returns false, except that two empty sequences compare equal. The method also returns a ClassCastException if any failure occurs evaluating either of the values.
      Overrides:
      equals in class Object
    • 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 type
      env - the static context
      whole - 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
    • 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
    • makeQNameValue

      public static QNameValue makeQNameValue(Object object, Configuration config)
      Temporary method to make a QNameValue from a JAXP 1.3 QName, without creating a compile-time link to the JDK 1.5 QName class
      Parameters:
      object - an instance of javax.xml.namespace.QName
      config - the Saxon configuration (used for dynamic loading)
      Returns:
      a corresponding Saxon QNameValue, or null if any error occurs performing the conversion
    • toString

      public String toString()
      Convert to a string for diagnostic output
      Overrides:
      toString in class Object
    • convertToJava

      public static 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