org.apache.commons.jxpath.ri.compiler
Class Expression

java.lang.Object
  org.apache.commons.jxpath.ri.compiler.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: 1.10 $ $Date: 2004/02/29 14:17:38 $

Author:

Dmitri Plotnikov

Nested Class Summary

static class	Expression.PointerIterator
static class	Expression.ValueIterator

Field Summary

private boolean	contextDependencyKnown
private boolean	contextDependent
protected static java.lang.Double	NOT_A_NUMBER
protected static java.lang.Double	ONE
protected static java.lang.Double	ZERO

Constructor Summary

Expression()

Method Summary

abstract java.lang.Object	compute(EvalContext context)
abstract boolean	computeContextDependent() Implemented by subclasses and result is cached by isContextDependent()
abstract java.lang.Object	computeValue(EvalContext context) Evaluates the expression.
boolean	isContextDependent() Returns true if this expression should be re-evaluated each time the current position in the context changes.
java.util.Iterator	iterate(EvalContext context)
java.util.Iterator	iteratePointers(EvalContext context)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

ZERO

protected static final java.lang.Double ZERO

ONE

protected static final java.lang.Double ONE

NOT_A_NUMBER

protected static final java.lang.Double NOT_A_NUMBER

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.

computeContextDependent

public abstract boolean computeContextDependent()

Implemented by subclasses and result is cached by isContextDependent()

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.

compute

public abstract java.lang.Object compute(EvalContext context)

iterate

public java.util.Iterator iterate(EvalContext context)

iteratePointers

public java.util.Iterator iteratePointers(EvalContext context)