net.sf.saxon.xpath

Class JAXPVariable

Implemented Interfaces:
Binding, VariableDeclaration

public final class JAXPVariable
extends java.lang.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

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()
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.

Constructor Details

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 Details

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

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

getRequiredType

public SequenceType getRequiredType()
Specified by:
getRequiredType in interface Binding

getVariableQName

public StructuredQName getVariableQName()
Get the name of the variable as a structured QName
Specified by:
getVariableQName in interface VariableDeclaration
getVariableQName in interface Binding

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

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

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