Class SingletonAtomizer

  • All Implemented Interfaces:
    java.io.Serializable, javax.xml.transform.SourceLocator, Container, Expression, InstructionInfoProvider

    public final class SingletonAtomizer
    extends UnaryExpression
    A SingletonAtomizer combines the functions of an Atomizer and a CardinalityChecker: it is used to atomize a sequence of nodes, checking that the result of the atomization contains zero or one atomic values. Note that the input may be a sequence of nodes or atomic values, even though the result must contain at most one atomic value.
    See Also:
    Serialized Form
    • Constructor Detail

      • SingletonAtomizer

        public SingletonAtomizer​(Expression sequence,
                                 RoleLocator role,
                                 boolean allowEmpty)
        Constructor
        Parameters:
        sequence - the sequence to be atomized
        allowEmpty - true if the result sequence is allowed to be empty.
    • Method Detail

      • typeCheck

        public Expression typeCheck​(StaticContext env,
                                    ItemType contextItemType)
                             throws XPathException
        Type-check the expression
        Specified by:
        typeCheck in interface Expression
        Overrides:
        typeCheck in class UnaryExpression
        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:
        StaticError - if an error is discovered during this phase (typically a type error)
        XPathException
      • getRole

        public RoleLocator getRole()
        Get the RoleLocator (used to construct error messages)
      • evaluateItem

        public Item evaluateItem​(XPathContext context)
                          throws XPathException
        Evaluate as an Item. This should only be called if the Atomizer has cardinality zero-or-one, which will only be the case if the underlying expression has cardinality zero-or-one.
        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
      • getItemType

        public ItemType getItemType​(TypeHierarchy th)
        Determine the data type of the items returned by the expression, if possible
        Specified by:
        getItemType in interface Expression
        Overrides:
        getItemType in class UnaryExpression
        Parameters:
        th -
        Returns:
        a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER. For this class, the result is always an atomic type, but it might be more specific.
      • displayOperator

        protected java.lang.String displayOperator​(Configuration config)
        Give a string representation of the operator for use in diagnostics
        Specified by:
        displayOperator in class UnaryExpression
        Parameters:
        config -
        Returns:
        the operator, as a string