Class ValueComparison

    • Constructor Detail

      • ValueComparison

        public ValueComparison​(Expression p1,
                               int op,
                               Expression p2)
        Create a comparison expression identifying the two operands and the operator
        Parameters:
        p1 - the left-hand operand
        op - the operator, as a token returned by the Tokenizer (e.g. Token.LT)
        p2 - the right-hand operand
    • Method Detail

      • getExpressionName

        public java.lang.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 explain() output displaying the expression.
      • setAtomicComparer

        public void setAtomicComparer​(AtomicComparer comparer)
        Set the AtomicComparer used to compare atomic values
        Parameters:
        comparer - the AtomicComparer
      • getAtomicComparer

        public AtomicComparer getAtomicComparer()
        Get the AtomicComparer used to compare atomic values. This encapsulates any collation that is used. Note that the comparer is always known at compile time.
        Specified by:
        getAtomicComparer in interface ComparisonExpression
      • getSingletonOperator

        public int getSingletonOperator()
        Get the primitive (singleton) operator used: one of Token.FEQ, Token.FNE, Token.FLT, Token.FGT, Token.FLE, Token.FGE
        Specified by:
        getSingletonOperator in interface ComparisonExpression
      • convertsUntypedToOther

        public boolean convertsUntypedToOther()
        Determine whether untyped atomic values should be converted to the type of the other operand
        Specified by:
        convertsUntypedToOther in interface ComparisonExpression
        Returns:
        true if untyped values should be converted to the type of the other operand, false if they should be converted to strings.
      • setResultWhenEmpty

        public void setResultWhenEmpty​(BooleanValue value)
        Set the result to be returned if one of the operands is an empty sequence
        Parameters:
        value - the result to be returned if an operand is empty. Supply null to mean the empty sequence.
      • getResultWhenEmpty

        public BooleanValue getResultWhenEmpty()
        Get the result to be returned if one of the operands is an empty sequence
        Returns:
        BooleanValue.TRUE, BooleanValue.FALSE, or null (meaning the empty sequence)
      • needsRuntimeComparabilityCheck

        public boolean needsRuntimeComparabilityCheck()
        Determine whether a run-time check is needed to check that the types of the arguments are comparable
        Returns:
        true if a run-time check is needed
      • typeCheck

        public Expression typeCheck​(ExpressionVisitor visitor,
                                    ExpressionVisitor.ContextItemType contextItemType)
                             throws XPathException
        Type-check the expression
        Overrides:
        typeCheck in class BinaryExpression
        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:
        the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations
        Throws:
        XPathException - if an error is discovered during this phase (typically a type error)
      • optimize

        public Expression optimize​(ExpressionVisitor visitor,
                                   ExpressionVisitor.ContextItemType 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.

        Overrides:
        optimize in class BinaryExpression
        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:
        the original expression, rewritten if appropriate to optimize execution
        Throws:
        XPathException - if an error is discovered during this phase (typically a type error)
      • isNegatable

        public boolean isNegatable​(ExpressionVisitor visitor)
        Check whether this specific instance of the expression is negatable
        Specified by:
        isNegatable in interface Negatable
        Returns:
        true if it is
      • negate

        public Expression negate()
        Return the negation of this value comparison: that is, a value comparison that returns true() if and only if the original returns false(). The result must be the same as not(this) even in the case where one of the operands is ().
        Specified by:
        negate in interface Negatable
        Returns:
        the inverted comparison
      • 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
      • effectiveBooleanValue

        public boolean effectiveBooleanValue​(XPathContext context)
                                      throws XPathException
        Evaluate the effective boolean value of the expression
        Overrides:
        effectiveBooleanValue in class Expression
        Parameters:
        context - the given context for evaluation
        Returns:
        a boolean representing the result of the comparison of the two operands
        Throws:
        XPathException - if any dynamic error occurs evaluating the expression
      • compare

        static boolean compare​(AtomicValue v0,
                               int op,
                               AtomicValue v1,
                               AtomicComparer comparer,
                               boolean checkTypes)
                        throws XPathException
        Compare two atomic values, using a specified operator and collation
        Parameters:
        v0 - the first operand
        op - the operator, as defined by constants such as Token.FEQ or Token.FLT
        v1 - the second operand
        comparer - the Collator to be used when comparing strings
        checkTypes -
        Returns:
        the result of the comparison: -1 for LT, 0 for EQ, +1 for GT
        Throws:
        XPathException - if the values are not comparable
      • evaluateItem

        public Item evaluateItem​(XPathContext context)
                          throws XPathException
        Evaluate the expression in a given context
        Overrides:
        evaluateItem in class Expression
        Parameters:
        context - the given context for evaluation
        Returns:
        a BooleanValue representing the result of the numeric comparison of the two operands, or null representing the empty sequence
        Throws:
        XPathException - if any dynamic error occurs evaluating the expression
      • getItemType

        public ItemType getItemType​(TypeHierarchy th)
        Determine the data type of the expression
        Specified by:
        getItemType in class Expression
        Parameters:
        th - the type hierarchy cache
        Returns:
        Type.BOOLEAN