Class Expression

  • Direct Known Subclasses:
    Constant, Operation, Path, VariableReference

    public abstract class Expression
    extends java.lang.Object
    Common superclass for several types of nodes in the parse tree. Provides APIs for optimization of evaluation of expressions. Specifically, an expression only needs to executed once during the evaluation of an xpath if that expression is context-independent. Expression.isContextDependent() provides that hint.
    Version:
    $Revision: 652845 $ $Date: 2008-05-02 12:46:46 -0500 (Fri, 02 May 2008) $
    • Field Detail

      • ZERO

        protected static final java.lang.Double ZERO
        zero
      • ONE

        protected static final java.lang.Double ONE
        one
      • NOT_A_NUMBER

        protected static final java.lang.Double NOT_A_NUMBER
        NaN
      • contextDependencyKnown

        private boolean contextDependencyKnown
      • contextDependent

        private boolean contextDependent
    • Constructor Detail

      • Expression

        public Expression()
    • Method Detail

      • isContextDependent

        public boolean isContextDependent()
        Returns true if this expression should be re-evaluated each time the current position in the context changes.
        Returns:
        boolean
      • computeContextDependent

        public abstract boolean computeContextDependent()
        Implemented by subclasses and result is cached by isContextDependent()
        Returns:
        calculated context-dependentness as boolean
      • computeValue

        public abstract java.lang.Object computeValue​(EvalContext context)
        Evaluates the expression. If the result is a node set, returns the first element of the node set.
        Parameters:
        context - evaluation context
        Returns:
        Object
      • compute

        public abstract java.lang.Object compute​(EvalContext context)
        Evaluates the expression. If the result is a node set, returns the first element of the node set.
        Parameters:
        context - evaluation context
        Returns:
        Object
      • iterate

        public java.util.Iterator iterate​(EvalContext context)
        Iterate over the values from the specified context.
        Parameters:
        context - evaluation context
        Returns:
        value Iterator
      • iteratePointers

        public java.util.Iterator iteratePointers​(EvalContext context)
        Iterate over the pointers from the specified context.
        Parameters:
        context - evaluation context
        Returns:
        pointer Iterator