Class FilterExpression

java.lang.Object
net.sf.saxon.expr.Expression
net.sf.saxon.expr.FilterExpression
All Implemented Interfaces:
Serializable, SourceLocator, LocationProvider, SaxonLocator, ContextSwitchingExpression, InstructionInfo, Locator
public final class FilterExpression extends Expression implements ContextSwitchingExpression
A FilterExpression contains a base expression and a filter predicate, which may be an integer expression (positional filter), or a boolean expression (qualifier)
See Also:

  • Field Details

  • Constructor Details

    • FilterExpression

      public FilterExpression(Expression start, Expression filter)
      Constructor
      Parameters:
      start - A node-set expression denoting the absolute or relative set of nodes from which the navigation path should start.
      filter - An expression defining the filter predicate

  • Method Details

    • getExpressionName

      public 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.

    • getItemType

      public ItemType getItemType(TypeHierarchy th)
      Get the data type of the items returned
      Specified by:
      getItemType in class Expression
      Parameters:
      th - the type hierarchy cache
      Returns:
      an integer representing the data type

    • getControllingExpression

      public Expression getControllingExpression()
      Get the underlying expression
      Specified by:
      getControllingExpression in interface ContextSwitchingExpression
      Returns:
      the expression being filtered

    • isFilterIsPositional

      public boolean isFilterIsPositional()
      Returns:
      the boolean of filter is positional
      See Also:
      • invalid reference 
        com.saxonica.bytecode.FilterExpressionCompiler

    • getControlledExpression

      public Expression getControlledExpression()
      Get the subexpression that is evaluated in the new context
      Specified by:
      getControlledExpression in interface ContextSwitchingExpression
      Returns:
      the subexpression evaluated in the context set by the controlling expression

    • getFilter

      public Expression getFilter()
      Get the filter expression
      Returns:
      the expression acting as the filter predicate

    • isPositional

      public boolean isPositional(TypeHierarchy th)
      Determine if the filter is positional
      Parameters:
      th - the Type Hierarchy (for cached access to type information)
      Returns:
      true if the value of the filter depends on the position of the item against which it is evaluated

    • isSimpleBooleanFilter

      public boolean isSimpleBooleanFilter()
      Test if the filter always returns a singleton boolean
      Returns:
      true if the filter is a simple boolean expression

    • isIndependentNumericFilter

      public boolean isIndependentNumericFilter()
      Determine whether the filter is a simple independent numeric, that is, an expression that satisfies the following conditions: (a) its value is numeric; (b) the value does not depend on the context item or position; (c) the cardinality is zero or one.
      Returns:
      true if the filter is a numeric value that does not depend on the context item or position

    • simplify

      public Expression simplify(ExpressionVisitor visitor) throws XPathException
      Simplify an expression
      Overrides:
      simplify in class Expression
      Parameters:
      visitor - the expression visitor
      Returns:
      the simplified expression
      Throws:
      XPathException - if any failure occurs

    • typeCheck

      public Expression typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) throws XPathException
      Type-check the expression
      Overrides:
      typeCheck in class Expression
      Parameters:
      visitor - the expression visitor
      contextItemType - the type of the context item for this expression
      Returns:
      the expression after type-checking (potentially modified to add run-time checks and/or conversions)
      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 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:
      the original expression, rewritten if appropriate to optimize execution
      Throws:
      XPathException - if an error is discovered during this phase (typically a type error)

    • 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.

    • 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 PathMapNodeSet to which the paths embodied in this expression should be added
      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

    • promote

      public Expression promote(PromotionOffer offer, Expression parent) throws XPathException
      Promote this expression if possible
      Overrides:
      promote in class Expression
      Parameters:
      offer - details of the promotion that is possible
      parent -
      Returns:
      the promoted expression (or the original expression, unchanged)
      Throws:
      XPathException - if any error is detected

    • iterateSubExpressions

      public Iterator<Expression> iterateSubExpressions()
      Get the immediate subexpressions of this expression
      Overrides:
      iterateSubExpressions in class Expression
      Returns:
      the subexpressions, as an array

    • iterateSameFocusSubExpressions

      public Iterator<Expression> iterateSameFocusSubExpressions()
      Get the immediate sub-expressions of this expression that are evaluated with the same focus (context item, position, and size) as the parent expression.
      Overrides:
      iterateSameFocusSubExpressions in class Expression
      Returns:
      an iterator containing those sub-expressions of this expression that are evaluated with the same focus as the parent expression

    • hasLoopingSubexpression

      public boolean hasLoopingSubexpression(Expression child)
      Given an expression that is an immediate child of this expression, test whether the evaluation of the parent expression causes the child expression to be evaluated repeatedly
      Overrides:
      hasLoopingSubexpression in class Expression
      Parameters:
      child - the immediate subexpression
      Returns:
      true if the child expression is evaluated repeatedly

    • replaceSubExpression

      public boolean replaceSubExpression(Expression original, Expression replacement)
      Replace one subexpression by a replacement subexpression
      Overrides:
      replaceSubExpression in class Expression
      Parameters:
      original - the original subexpression
      replacement - the replacement subexpression
      Returns:
      true if the original subexpression is found

    • computeCardinality

      public int computeCardinality()
      Get the static cardinality of this expression
      Specified by:
      computeCardinality in class Expression
      Returns:
      the cardinality. The method attempts to determine the case where the filter predicate is guaranteed to select at most one item from the sequence being filtered

    • computeSpecialProperties

      public int computeSpecialProperties()
      Get the static properties of this expression (other than its type). The result is bit-significant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.
      Overrides:
      computeSpecialProperties in class Expression
      Returns:
      the static properties of the expression, as a bit-significant value

    • equals

      public boolean equals(Object other)
      Is this expression the same as another expression?
      Overrides:
      equals in class Object
      Parameters:
      other - the expression to be compared with this one
      Returns:
      true if the two expressions are statically equivalent

    • hashCode

      public int hashCode()
      get HashCode for comparing two expressions
      Overrides:
      hashCode in class Object
      Returns:
      the hash code

    • iterate

      public SequenceIterator iterate(XPathContext context) throws XPathException
      Iterate over the results, returning them in the correct order
      Overrides:
      iterate in class Expression
      Parameters:
      context - the dynamic context for the evaluation
      Returns:
      an iterator over the expression results
      Throws:
      XPathException - if any dynamic error occurs

    • computeDependencies

      public int computeDependencies()
      Determine which aspects of the context the expression depends on. The result is a bitwise-or'ed value composed from constants such as XPathContext.VARIABLES and XPathContext.CURRENT_NODE
      Overrides:
      computeDependencies in class Expression
      Returns:
      the dependencies

    • 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

    • 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 ExpressionPresenter to be used