Class Literal

All Implemented Interfaces:
Serializable, SourceLocator, LocationProvider, SaxonLocator, InstructionInfo, Locator
Direct Known Subclasses:
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 Value. 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')
See Also:
  • Constructor Details

    • Literal

      public Literal(Value value)
      Create a literal as a wrapper around a Value
      Parameters:
      value - the value of this literal
  • Method Details

    • makeLiteral

      public static Literal makeLiteral(Value value)
      Create a literal as a wrapper around a Value (factory method)
      Parameters:
      value - the value of this literal
      Returns:
      the Literal
    • makeEmptySequence

      public static Literal makeEmptySequence()
      Make an empty-sequence literal
      Returns:
      a literal whose value is the empty sequence
    • getValue

      public Value getValue()
      Get the value represented by this Literal
      Returns:
      the constant value
    • simplify

      public Expression simplify(ExpressionVisitor visitor)
      Simplify an expression
      Overrides:
      simplify in class Expression
      Parameters:
      visitor - an expression visitor
      Returns:
      for a Value, this always returns the value unchanged
    • typeCheck

      public Expression typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType)
      TypeCheck an expression
      Overrides:
      typeCheck 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
    • optimize

      public final Expression optimize(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType)
      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
    • getItemType

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

      public 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
    • computeSpecialProperties

      public int computeSpecialProperties()
      Compute the static properties of this expression (other than its type). For a Value, the only special property is StaticProperty.NON_CREATIVE.
      Overrides:
      computeSpecialProperties in class Expression
      Returns:
      the value StaticProperty.NON_CREATIVE
    • 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()
      Copy an expression. This makes a deep copy.
      Specified by:
      copy in class Expression
      Returns:
      the copy of the original expression
    • 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<? extends Item> 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<? extends Item> 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(XPathContext context) throws XPathException
      Process the value as an instruction, without returning any tail calls
      Overrides:
      process in class Expression
      Parameters:
      context - The dynamic context, giving access to the current node, the current variables, etc.
      Throws:
      XPathException - if a dynamic error occurs
    • evaluateAsString

      public CharSequence 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
    • evaluatePendingUpdates

      public void evaluatePendingUpdates(XPathContext context, PendingUpdateList pul) throws XPathException
      Evaluate an updating expression, adding the results to a Pending Update List. The default implementation of this method, which is used for non-updating expressions, throws an UnsupportedOperationException. The implementation for a literal representing an empty sequence, however, is a no-op.
      Overrides:
      evaluatePendingUpdates in class Expression
      Parameters:
      context - the XPath dynamic evaluation context
      pul - the pending update list to which the results should be written
      Throws:
      XPathException - if evaluation fails
    • equals

      public boolean equals(Object obj)
      Determine whether two literals are equal, when considered as expressions.
      Overrides:
      equals in class Object
      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.
    • hashCode

      public int hashCode()
      Return a hash code to support the equals() function
      Overrides:
      hashCode in class Object
    • 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
    • explain

      public void explain(ExpressionPresenter out)
      Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
      Specified by:
      explain in class Expression
      Parameters:
      out - the expression presenter used to display the structure
    • 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:
      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:
      if the expression is a literal and the literal wraps an AtomicValue
    • 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:
      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:
      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.