net.sf.saxon.xpath
Class JAXPVariable

java.lang.Object
  net.sf.saxon.xpath.JAXPVariable

All Implemented Interfaces:

Binding, VariableDeclaration

public final class JAXPVariable
extends Object
implements VariableDeclaration, Binding

An object representing an XPath variable for use in the JAXP XPath API. The object is created at compile time when the parser tries to bind a variable reference; the value is fetched at run-time from the XPathVariableResolver. With this interface, there is no way of reporting a static error if the variable has not been declared.

In Saxon terms, this class is both a VariableDeclaration and a Binding. Unlike a normal VariableDeclaration, it isn't created in advance, but is created on demand when the parser encounters a variable reference. This actually means that if the XPath expression contains two references to the same variable, two VariableDeclarations will be created; however, they will be indistinguishable to the VariableResolver. Acting as a VariableDeclaration, the object goes through the motions of fixing up a binding to a variable reference (in practice, of course, there is exactly one reference to the variable). Acting as a run-time binding, it then evaluates the variable by calling the XPathVariableResolver supplied by the API caller. If no XPathVariableResolver was supplied, an error is reported when a variable is encountered; but if the variable resolver doesn't recognize the variable name, it returns null, which is treated as an empty sequence.

Constructor Summary

protected

JAXPVariable(StructuredQName name, XPathVariableResolver resolver) Private constructor: for use only be the protected factory method make()

Method Summary

ValueRepresentation	evaluateVariable(XPathContext context) Get the value of the variable.
int	getLocalSlotNumber() If this is a local variable held on the local stack frame, return the corresponding slot number.
SequenceType	getRequiredType() Get the declared type of the variable
StructuredQName	getVariableQName() Get the name of the variable as a structured QName
boolean	isAssignable() Test whether it is permitted to assign to the variable using the saxon:assign extension element.
boolean	isGlobal() Indicate whether the binding is local or global.
void	registerReference(BindingReference ref) Method called by the XPath expression parser to register a reference to this variable.

Methods inherited from class java.lang.Object

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

Constructor Detail

JAXPVariable

protected JAXPVariable(StructuredQName name,
                       XPathVariableResolver resolver)

Private constructor: for use only be the protected factory method make()

Parameters:

name - the name of the variable

resolver - the resolver used in conjunction with this variable

Method Detail

getRequiredType

public SequenceType getRequiredType()

Description copied from interface: Binding

Get the declared type of the variable

Specified by:

getRequiredType in interface Binding

Returns:

the declared type

isGlobal

public boolean isGlobal()

Indicate whether the binding is local or global. A global binding is one that has a fixed value for the life of a query or transformation; any other binding is local.

Specified by:

isGlobal in interface Binding

Returns:

true if the binding is global

isAssignable

public final boolean isAssignable()

Test whether it is permitted to assign to the variable using the saxon:assign extension element. This will only be for an XSLT global variable where the extra attribute saxon:assignable="yes" is present.

Specified by:

isAssignable in interface Binding

Returns:

true if the binding is assignable

getLocalSlotNumber

public int getLocalSlotNumber()

If this is a local variable held on the local stack frame, return the corresponding slot number. In other cases, return -1.

Specified by:

getLocalSlotNumber in interface Binding

Returns:

the slot number on the local stack frame

getVariableQName

public StructuredQName getVariableQName()

Get the name of the variable as a structured QName

Specified by:

getVariableQName in interface Binding

Specified by:

getVariableQName in interface VariableDeclaration

Returns:

the variable name

registerReference

public void registerReference(BindingReference ref)

Method called by the XPath expression parser to register a reference to this variable. This method should not be called by users of the API.

Specified by:

registerReference in interface VariableDeclaration

Parameters:

ref - the variable reference

evaluateVariable

public ValueRepresentation evaluateVariable(XPathContext context)
                                     throws XPathException

Get the value of the variable. This method is used by the XPath execution engine to retrieve the value.

Specified by:

evaluateVariable in interface Binding

Parameters:

context - The dynamic evaluation context

Returns:

The value of the variable

Throws:

XPathException