Package net.sf.saxon.expr

Class Literal

java.lang.Object
net.sf.saxon.expr.Expression
net.sf.saxon.expr.Literal
All Implemented Interfaces:
ExportAgent, Locatable, IdentityComparable, Traceable
Direct Known Subclasses:
FunctionLiteral, StringLiteral
public class Literal extends Expression
A Literal is an expression whose value is constant: it is a class that implements the Expression interface as a wrapper around a GroundedValue. This may derive from an actual literal in an XPath expression or query, or it may be the result of evaluating a constant subexpression such as true() or xs:date('2007-01-16')

  • Constructor Details

    • Literal

      protected Literal(GroundedValue value)
      Create a literal as a wrapper around a Value
      Parameters:
      value - the value of this literal

  • Method Details

    • getGroundedValue

      public GroundedValue getGroundedValue()
      Get the value represented by this Literal
      Returns:
      the constant value

    • typeCheck

      public Expression typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) throws XPathException
      TypeCheck an expression
      Overrides:
      typeCheck in class Expression
      Parameters:
      visitor - an expression visitor
      contextInfo - Information available statically about the context item: whether it is (possibly) absent; its static type; its streaming posture.
      Returns:
      for a Value, this always returns the value unchanged
      Throws:
      XPathException - if an error is discovered during this phase (typically a type error)

    • optimize

      public Expression optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType) throws XPathException
      Optimize an expression
      Overrides:
      optimize in class Expression
      Parameters:
      visitor - an expression visitor
      contextItemType - the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set to Type.ITEM_TYPE
      Returns:
      for a Value, this always returns the value unchanged
      Throws:
      XPathException - if an error is discovered during this phase (typically a type error)

    • getNetCost

      public int getNetCost()
      Return the estimated cost of evaluating an expression. This is a very crude measure based on the syntactic form of the expression (we have no knowledge of data values). We take the cost of evaluating a simple scalar comparison or arithmetic expression as 1 (one), and we assume that a sequence has length 5. The resulting estimates may be used, for example, to reorder the predicates in a filter expression so cheaper predicates are evaluated first.
      Overrides:
      getNetCost in class Expression
      Returns:
      the intrinsic cost of this operation, excluding the costs of evaluating the operands

    • getItemType

      public ItemType getItemType()
      Determine the data type of the items in the expression, if possible
      Specified by:
      getItemType in class Expression
      Returns:
      for the default implementation: AnyItemType (not known)

    • isInstance

      public boolean isInstance(SequenceType req, TypeHierarchy th)

    • getStaticUType

      public UType getStaticUType(UType contextItemType)
      Get the static type of the expression as a UType, following precisely the type inference rules defined in the XSLT 3.0 specification.
      Overrides:
      getStaticUType in class Expression
      Parameters:
      contextItemType - the static context item type
      Returns:
      the static item type of the expression according to the XSLT 3.0 defined rules

    • computeCardinality

      protected int computeCardinality()
      Determine the cardinality
      Specified by:
      computeCardinality in class Expression
      Returns:
      the computed cardinality, as one of the values StaticProperty.ALLOWS_ZERO_OR_ONE, StaticProperty.EXACTLY_ONE, StaticProperty.ALLOWS_ONE_OR_MORE, StaticProperty.ALLOWS_ZERO_OR_MORE. May also return StaticProperty.ALLOWS_ZERO if the result is known to be an empty sequence, or StaticProperty.ALLOWS_MANY if if is known to return a sequence of length two or more.

    • computeSpecialProperties

      protected int computeSpecialProperties()
      Compute the static properties of this expression (other than its type). For a Value, the only special property is StaticProperty.NO_NODES_NEWLY_CREATED.
      Overrides:
      computeSpecialProperties in class Expression
      Returns:
      the value StaticProperty.NO_NODES_NEWLY_CREATED

    • supportsLazyEvaluation

      public boolean supportsLazyEvaluation()
      Ask whether the expression supports lazy evaluation.
      Overrides:
      supportsLazyEvaluation in class Expression
      Returns:
      false either if the expression cannot be evaluated lazily because it has dependencies that cannot be saved in the context, or because lazy evaluation is pointless (for example, for literals and variable references).

    • getIntegerBounds

      public IntegerValue[] getIntegerBounds()
      For an expression that returns an integer or a sequence of integers, get a lower and upper bound on the values of the integers that may be returned, from static analysis. The default implementation returns null, meaning "unknown" or "not applicable". Other implementations return an array of two IntegerValue objects, representing the lower and upper bounds respectively. The values UNBOUNDED_LOWER and UNBOUNDED_UPPER are used by convention to indicate that the value may be arbitrarily large. The values MAX_STRING_LENGTH and MAX_SEQUENCE_LENGTH are used to indicate values limited by the size of a string or the size of a sequence.
      Overrides:
      getIntegerBounds in class Expression
      Returns:
      the lower and upper bounds of integer values in the result, or null to indicate unknown or not applicable.

    • isVacuousExpression

      public boolean isVacuousExpression()
      Determine whether this is a vacuous expression as defined in the XQuery update specification
      Overrides:
      isVacuousExpression in class Expression
      Returns:
      true if this expression is vacuous

    • copy

      public Expression copy(RebindingMap rebindings)
      Copy an expression. This makes a deep copy.
      Specified by:
      copy in class Expression
      Parameters:
      rebindings - variables that need to be re-bound
      Returns:
      a copy of the original literal. Note that the underlying value is not copied; the code relies on the caller treating the underlying value as immutable.

    • toPattern

      public Pattern toPattern(Configuration config) throws XPathException
      Convert this expression to an equivalent XSLT pattern
      Overrides:
      toPattern in class Expression
      Parameters:
      config - the Saxon configuration
      Returns:
      the equivalent pattern
      Throws:
      XPathException - if conversion is not possible

    • addToPathMap

      public PathMap.PathMapNodeSet addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)
      Add a representation of this expression to a PathMap. The PathMap captures a map of the nodes visited by an expression in a source tree.
      Overrides:
      addToPathMap in class Expression
      Parameters:
      pathMap - the PathMap to which the expression should be added
      pathMapNodeSet - the set of nodes within the path map
      Returns:
      the pathMapNode representing the focus established by this expression, in the case where this expression is the first operand of a path expression or filter expression

    • getDependencies

      public final int getDependencies()
      Determine which aspects of the context the expression depends on. The result is a bitwise-or'ed value composed from constants such as StaticProperty.VARIABLES and StaticProperty.CURRENT_NODE
      Overrides:
      getDependencies in class Expression
      Returns:
      for a Value, this always returns zero.

    • iterate

      public SequenceIterator iterate(XPathContext context) throws XPathException
      Return an Iterator to iterate over the values of a sequence. The value of every expression can be regarded as a sequence, so this method is supported for all expressions. This default implementation handles iteration for expressions that return singleton values: for non-singleton expressions, the subclass must provide its own implementation.
      Overrides:
      iterate in class Expression
      Parameters:
      context - supplies the context for evaluation
      Returns:
      a SequenceIterator that can be used to iterate over the result of the expression
      Throws:
      XPathException - if any dynamic error occurs evaluating the expression

    • iterate

      public SequenceIterator iterate() throws XPathException
      Return an Iterator to iterate over the values of a sequence. The value of every expression can be regarded as a sequence, so this method is supported for all expressions. This default implementation handles iteration for expressions that return singleton values: for non-singleton expressions, the subclass must provide its own implementation.
      Returns:
      a SequenceIterator that can be used to iterate over the result of the expression
      Throws:
      XPathException - if any dynamic error occurs evaluating the expression

    • evaluateItem

      public Item evaluateItem(XPathContext context) throws XPathException
      Evaluate as a singleton item (or empty sequence). Note: this implementation returns the first item in the sequence. The method should not be used unless appropriate type-checking has been done to ensure that the value will be a singleton.
      Overrides:
      evaluateItem in class Expression
      Parameters:
      context - The context in which the expression is to be evaluated
      Returns:
      the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence
      Throws:
      XPathException - if any dynamic error occurs evaluating the expression

    • process

      public void process(Outputter output, XPathContext context) throws XPathException
      Process the value as an instruction, without returning any tail calls
      Overrides:
      process in class Expression
      Parameters:
      output - the destination for the result
      context - The dynamic context, giving access to the current node,
      Throws:
      XPathException - if a dynamic error occurs

    • getImplementationMethod

      public int getImplementationMethod()
      Description copied from class: Expression
      An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is provided directly. The other methods will always be available indirectly, using an implementation that relies on one of the other methods.
      Specified by:
      getImplementationMethod in class Expression
      Returns:
      the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

    • evaluateAsString

      public UnicodeString evaluateAsString(XPathContext context) throws XPathException
      Description copied from class: Expression
      Evaluate an expression as a String. This function must only be called in contexts where it is known that the expression will return a single string (or where an empty sequence is to be treated as a zero-length string). Implementations should not attempt to convert the result to a string, other than converting () to "". This method is used mainly to evaluate expressions produced by compiling an attribute value template.
      Overrides:
      evaluateAsString in class Expression
      Parameters:
      context - The context in which the expression is to be evaluated
      Returns:
      the value of the expression, evaluated in the current context. The expression must return a string or (); if the value of the expression is (), this method returns "".
      Throws:
      XPathException - if any dynamic error occurs evaluating the expression

    • effectiveBooleanValue

      public boolean effectiveBooleanValue(XPathContext context) 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.
      Overrides:
      effectiveBooleanValue in class Expression
      Parameters:
      context - The context in which the expression is to be evaluated
      Returns:
      the effective boolean value
      Throws:
      XPathException - if any dynamic error occurs evaluating the expression

    • equals

      public boolean equals(Object obj)
      Determine whether two literals are equal, when considered as expressions.
      Overrides:
      equals in class Expression
      Parameters:
      obj - the other expression
      Returns:
      true if the two literals are equal. The test here requires (a) identity in the sense defined by XML Schema (same value in the same value space), and (b) identical type annotations. For example the literal xs:int(3) is not equal (as an expression) to xs:short(3), because the two expressions are not interchangeable.

    • computeHashCode

      protected int computeHashCode()
      Return a hash code to support the equals() function
      Overrides:
      computeHashCode in class Expression
      Returns:
      a computed hash code

    • toString

      public String toString()
      The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath. In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax
      Overrides:
      toString in class Expression
      Returns:
      a representation of the expression as a string

    • export

      public void export(ExpressionPresenter out) throws XPathException
      Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
      Specified by:
      export in interface ExportAgent
      Specified by:
      export in class Expression
      Parameters:
      out - the expression presenter used to display the structure
      Throws:
      XPathException - if the export fails, for example if an expression is found that won't work in the target environment.

    • exportValue

      public static void exportValue(Sequence value, ExpressionPresenter out) throws XPathException
      Throws:
      XPathException

    • getExpressionName

      public String getExpressionName()
      Get a name identifying the kind of expression, in terms meaningful to a user.
      Overrides:
      getExpressionName in class Expression
      Returns:
      a name identifying the kind of expression, in terms meaningful to a user. The name will always be in the form of a lexical XML QName, and should match the name used in export() output displaying the expression.

    • exportAtomicValue

      public static void exportAtomicValue(AtomicValue value, ExpressionPresenter out) throws XPathException
      Throws:
      XPathException

    • toShortString

      public String toShortString()
      Produce a short string identifying the expression for use in error messages
      Overrides:
      toShortString in class Expression
      Returns:
      a short string, sufficient to identify the expression

    • isAtomic

      public static boolean isAtomic(Expression exp)
      Test whether the literal wraps an atomic value. (Note, if this method returns false, this still leaves the possibility that the literal wraps a sequence that happens to contain a single atomic value).
      Parameters:
      exp - an expression
      Returns:
      true if the expression is a literal and the literal wraps an AtomicValue

    • isEmptySequence

      public static boolean isEmptySequence(Expression exp)
      Test whether the literal explicitly wraps an empty sequence. (Note, if this method returns false, this still leaves the possibility that the literal wraps a sequence that happens to be empty).
      Parameters:
      exp - an expression
      Returns:
      true if the expression is a literal and the value of the literal is an empty sequence

    • isConstantBoolean

      public static boolean isConstantBoolean(Expression exp, boolean value)
      Test if a literal represents the boolean value true
      Parameters:
      exp - an expression
      value - true or false
      Returns:
      true if the expression is a literal and the literal represents the boolean value given in the second argument

    • hasEffectiveBooleanValue

      public static boolean hasEffectiveBooleanValue(Expression exp, boolean value)
      Test if a literal has the effective boolean value true (or false)
      Parameters:
      exp - an expression
      value - true or false
      Returns:
      true if the expression is a literal and the literal represents the boolean value given in the second argument

    • isConstantOne

      public static boolean isConstantOne(Expression exp)
      Test if a literal represents the integer value 1
      Parameters:
      exp - an expression
      Returns:
      true if the expression is a literal and the literal represents the integer value 1

    • isConstantZero

      public static boolean isConstantZero(Expression exp)
      Test if a literal represents the integer value 1
      Parameters:
      exp - an expression
      Returns:
      true if the expression is a literal and the literal represents the integer value 1

    • isSubtreeExpression

      public boolean isSubtreeExpression()
      Determine whether the expression can be evaluated without reference to the part of the context document outside the subtree rooted at the context node.
      Overrides:
      isSubtreeExpression in class Expression
      Returns:
      true if the expression has no dependencies on the context node, or if the only dependencies on the context node are downward selections using the self, child, descendant, attribute, and namespace axes.

    • makeEmptySequence

      public static Literal makeEmptySequence()
      Factory method to make an empty-sequence literal
      Returns:
      a literal whose value is the empty sequence

    • makeLiteral

      public static Literal makeLiteral(GroundedValue value)
      Factory method to create a literal as a wrapper around a Value (factory method)
      Parameters:
      value - the value of this literal
      Returns:
      the Literal

    • makeLiteral

      public static Literal makeLiteral(GroundedValue value, Expression origin)
      Make a literal, taking the retained static context and location information from another expression which is being simplified/optimized
      Parameters:
      value - the literal value
      origin - the expression whose context and location information is to be retained
      Returns:
      the Literal

    • getStreamerName

      public String getStreamerName()
      Get the (partial) name of a class that supports streaming of this kind of expression
      Overrides:
      getStreamerName in class Expression
      Returns:
      the partial name of a class that can be instantiated to provide streaming support in Saxon-EE, or null if there is no such class

    • getElaborator

      public Elaborator getElaborator()
      Make an elaborator for this expression
      Overrides:
      getElaborator in class Expression
      Returns:
      a suitable elaborator