Class FilterExpression

java.lang.Object
net.sf.saxon.expr.ComputedExpression
net.sf.saxon.expr.FilterExpression
All Implemented Interfaces:
Serializable, SourceLocator, Container, Expression, InstructionInfoProvider

public final class FilterExpression extends ComputedExpression
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:
  • 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

    • getItemType

      public ItemType getItemType(TypeHierarchy th)
      Get the data type of the items returned
      Parameters:
      th -
      Returns:
      an integer representing the data type
    • getBaseExpression

      public Expression getBaseExpression()
      Get the underlying expression
      Returns:
      the expression being filtered
    • 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
    • simplify

      public Expression simplify(StaticContext env) throws XPathException
      Simplify an expression
      Specified by:
      simplify in interface Expression
      Overrides:
      simplify in class ComputedExpression
      Parameters:
      env - the static context
      Returns:
      the simplified expression
      Throws:
      XPathException - if any failure occurs
    • typeCheck

      public Expression typeCheck(StaticContext env, ItemType contextItemType) throws XPathException
      Type-check the expression
      Parameters:
      env - the static context
      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 expression after type-checking (potentially modified to add run-time checks and/or conversions)
      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
    • promote

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

      public Iterator iterateSubExpressions()
      Get the immediate subexpressions of this expression
      Specified by:
      iterateSubExpressions in interface Expression
      Overrides:
      iterateSubExpressions in class ComputedExpression
      Returns:
      the subexpressions, as an array
    • replaceSubExpression

      public boolean replaceSubExpression(Expression original, Expression replacement)
      Replace one subexpression by a replacement subexpression
      Specified by:
      replaceSubExpression in interface Container
      Overrides:
      replaceSubExpression in class ComputedExpression
      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 ComputedExpression
      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 ComputedExpression
      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
      Specified by:
      iterate in interface Expression
      Overrides:
      iterate in class ComputedExpression
      Parameters:
      context - the dynamic context for the evaluation
      Returns:
      an iterator over the expression results
      Throws:
      XPathException - if any dynamic error occurs
    • isIndexable

      public boolean isIndexable()
      Test whether the filter is amenable to indexing
    • 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 ComputedExpression
      Returns:
      the dependencies
    • display

      public void display(int level, PrintStream out, Configuration config)
      Diagnostic print of expression structure
      Parameters:
      level - the indentation level
      out -
      config -