Class ValueComparison

All Implemented Interfaces:
Serializable, SourceLocator, ComparisonExpression, Container, Expression, InstructionInfoProvider

public final class ValueComparison extends BinaryExpression implements ComparisonExpression
ValueComparison: a boolean expression that compares two atomic values for equals, not-equals, greater-than or less-than. Implements the operators eq, ne, lt, le, gt, ge
See Also:
  • Constructor Details

    • ValueComparison

      public ValueComparison(Expression p1, int op, Expression p2)
      Create a relational 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 Details

    • getAtomicComparer

      public AtomicComparer getAtomicComparer()
      Get the AtomicComparer used to compare atomic values. This encapsulates any collation that is used
      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
    • getResultWhenEmpty

      public BooleanValue getResultWhenEmpty()
      Get the result to be returned if one of the operands is an empty sequence
    • typeCheck

      public Expression typeCheck(StaticContext env, ItemType contextItemType) throws XPathException
      Type-check the expression
      Specified by:
      typeCheck in interface Expression
      Overrides:
      typeCheck in class BinaryExpression
      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.

      Specified by:
      optimize in interface Expression
      Overrides:
      optimize in class BinaryExpression
      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
    • negate

      public ValueComparison 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 ().
    • effectiveBooleanValue

      public boolean effectiveBooleanValue(XPathContext context) throws XPathException
      Evaluate the effective boolean value of the expression
      Specified by:
      effectiveBooleanValue in interface Expression
      Overrides:
      effectiveBooleanValue in class ComputedExpression
      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 v1, int op, AtomicValue v2, AtomicComparer collator) throws DynamicError
      Compare two atomic values, using a specified operator and collation
      Parameters:
      v1 - the first operand
      op - the operator, as defined by constants such as Token.FEQ or Token.FLT
      v2 - the second operand
      collator - the Collator to be used when comparing strings
      Throws:
      DynamicError - if the values are not comparable
    • evaluateItem

      public Item evaluateItem(XPathContext context) throws XPathException
      Evaluate the expression in a given context
      Specified by:
      evaluateItem in interface Expression
      Overrides:
      evaluateItem in class ComputedExpression
      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 interface Expression
      Parameters:
      th -
      Returns:
      Type.BOOLEAN
    • computeCardinality

      public int computeCardinality()
      Determine the static cardinality.
      Overrides:
      computeCardinality in class BinaryExpression
    • displayOperator

      protected String displayOperator()
      Overrides:
      displayOperator in class BinaryExpression