Package 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: 652845 $ $Date: 2008-05-02 12:46:46 -0500 (Fri, 02 May 2008) $

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	Expression.PointerIterator	Pointer iterator
static class	Expression.ValueIterator	Value Iterator

Field Summary

Fields

Modifier and Type	Field	Description
private boolean	contextDependencyKnown
private boolean	contextDependent
protected static java.lang.Double	NOT_A_NUMBER	NaN
protected static java.lang.Double	ONE	one
protected static java.lang.Double	ZERO	zero

Constructor Summary

Constructors

Constructor	Description
Expression()

Method Summary

Modifier and Type	Method	Description
abstract java.lang.Object	compute(EvalContext context)	Evaluates the expression.
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)	Iterate over the values from the specified context.
java.util.Iterator	iteratePointers(EvalContext context)	Iterate over the pointers from the specified 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

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