net.sf.saxon.xpath

Class JAXPVariable

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
ValueRepresentationevaluateVariable(XPathContext context)
Get the value of the variable.
intgetLocalSlotNumber()
If this is a local variable held on the local stack frame, return the corresponding slot number.
SequenceTypegetRequiredType()
StructuredQNamegetVariableQName()
Get the name of the variable as a structured QName
booleanisAssignable()
Test whether it is permitted to assign to the variable using the saxon:assign extension element.
booleanisGlobal()
Indicate whether the binding is local or global.
QNamemakeQName(QNameValue in)
Construct a JAXP QName from a Saxon QNameValue
voidregisterReference(BindingReference ref)
Method called by the XPath expression parser to register a reference to this variable.

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

evaluateVariable

public ValueRepresentation evaluateVariable(XPathContext context)
Get the value of the variable. This method is used by the XPath execution engine to retrieve the value.

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.

getRequiredType

public SequenceType getRequiredType()

getVariableQName

public StructuredQName getVariableQName()
Get the name of the variable as a structured QName

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.

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.

makeQName

QName makeQName(QNameValue in)
Construct a JAXP QName from a Saxon QNameValue

Parameters: in the Saxon QNameValue

Returns: the JAXP QName

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.