Class SingleNodeExpression

java.lang.Object
net.sf.saxon.expr.ComputedExpression
net.sf.saxon.expr.SingleNodeExpression
All Implemented Interfaces:
Serializable, SourceLocator, Container, Expression, InstructionInfoProvider
Direct Known Subclasses:
ParentNodeExpression, RootExpression

public abstract class SingleNodeExpression extends ComputedExpression
A node set expression that will always return zero or one nodes
See Also:
  • Constructor Details

    • SingleNodeExpression

      public SingleNodeExpression()
  • Method Details

    • typeCheck

      public Expression typeCheck(StaticContext env, ItemType contextItemType) throws XPathException
      Type-check the expression.
      Parameters:
      env - the static context of the expression
      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:
      the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations
      Throws:
      XPathException
    • optimize

      public Expression optimize(Optimizer opt, StaticContext env, ItemType contextItemType) throws XPathException
      Perform optimisation of an expression and its subexpressions.

      This method is called after all references to functions and variables have been resolved to the declaration of the function or variable, and after all type checking has been done.

      Parameters:
      opt - the optimizer in use. This provides access to supporting functions; it also allows different optimization strategies to be used in different circumstances.
      env - the static context of the expression
      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:
      the original expression, rewritten if appropriate to optimize execution
      Throws:
      StaticError - if an error is discovered during this phase (typically a type error)
      XPathException
    • computeCardinality

      public int computeCardinality()
      Specify that the expression returns a singleton
      Specified by:
      computeCardinality in class ComputedExpression
    • getItemType

      public ItemType getItemType(TypeHierarchy th)
      Determine the data type of the items returned by this expression
      Parameters:
      th -
      Returns:
      Type.NODE
    • getIntrinsicDependencies

      public int getIntrinsicDependencies()
      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:
      getIntrinsicDependencies in class ComputedExpression
      Returns:
      a set of bit-significant flags identifying the "intrinsic" dependencies. The flags are documented in class net.sf.saxon.value.StaticProperty
    • computeSpecialProperties

      public int computeSpecialProperties()
      Overrides:
      computeSpecialProperties in class ComputedExpression
    • getNode

      public abstract NodeInfo getNode(XPathContext context) throws XPathException
      Get the single node to which this expression refers. Returns null if the node-set is empty
      Throws:
      XPathException
    • iterate

      public SequenceIterator iterate(XPathContext context) throws XPathException
      Evaluate the expression in a given context to return an iterator
      Specified by:
      iterate in interface Expression
      Overrides:
      iterate in class ComputedExpression
      Parameters:
      context - the evaluation context
      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
      Description copied from class: ComputedExpression
      Evaluate an expression as a single item. This always returns either a single Item or null (denoting the empty sequence). No conversion is done. This method should not be used unless the static type of the expression is a subtype of "item" or "item?": that is, it should not be called if the expression may return a sequence. There is no guarantee that this condition will be detected.
      Specified by:
      evaluateItem in interface Expression
      Overrides:
      evaluateItem in class ComputedExpression
      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
    • effectiveBooleanValue

      public boolean effectiveBooleanValue(XPathContext context) throws XPathException
      Description copied from class: ComputedExpression
      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.
      Specified by:
      effectiveBooleanValue in interface Expression
      Overrides:
      effectiveBooleanValue in class ComputedExpression
      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