com.novell.xml.xpath
Class Function

java.lang.Object
  com.novell.xml.xpath.Function

Direct Known Subclasses:

BadFunction, ECMAScriptFunction, JavaInstance, JavaMember, xpathBoolean, xpathCeiling, xpathConcat, xpathContains, xpathCount, xpathFalse, xpathFloor, xpathId, xpathLang, xpathLast, xpathLocalName, xpathName, xpathNamespaceUri, xpathNormalizeSpace, xpathNot, xpathNumber, xpathPosition, xpathRound, xpathStartsWith, xpathString, xpathStringLength, xpathSubstring, xpathSubstringAfter, xpathSubstringBefore, xpathSum, xpathTranslate, xpathTrue, xsltCurrent, xsltDocument, xsltElementAvailable, xsltFormatNumber, xsltFunctionAvailable, xsltGenerateId, xsltKey, xsltSystemProperty, xsltUnparsedEntityURI

public abstract class Function

extends Object

This class provides the basic common implementation for XPath functions. Functions in XPath must be derived from this class. The basic method of implementing a function is to derive a class from this class and provide one or more public methods for the implementation of the function. If the default invoke() member is not overridden the must be a separate, public member for each combination of arguments (required and optional). The default invoke member() uses introspection to find the methods in derived classes that match the function signature. This method information is cached, and is not calculated until the first invocation. However, better performance can probably be gained by over- riding invoke(). For functions that take different types of arguments, invoke() must be overridden (e.g., XPath's string(), boolean(), number(), and id() functions, which are defined to take any of the four basic types).

See Also:

FunctionSignature, FunctionCall

Constructor Summary

protected

Function(FunctionSignature signature) Construct a Function with the passed signature

Method Summary

Function	getInstance(ArgumentList args) Return an instance of this function that matches the passed argument list.
protected FunctionSignature	getSignature() Return the signature for this Function.
ExpressionValue	invoke(Object[] args) Invoke the function using the passed list of arguments.
boolean	isConstant() Return true if the expression is a constant value.
void	registerForReset(XPathResetRegistrar registrar) Register this expression or any subexpression that implements XPathResetCache with an object that wants to call resetCache()

Methods inherited from class java.lang.Object

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

Constructor Detail

Function

protected Function(FunctionSignature signature)

Construct a Function with the passed signature

Parameters:

signature - Object describing return type, name, and arguments

Method Detail

getInstance

public Function getInstance(ArgumentList args)
                     throws XPathParserException

Return an instance of this function that matches the passed argument list. This is intended primarily to be overridden in support of extension functions

Parameters:

args - The argument list

Throws:

XPathParserException

invoke

public ExpressionValue invoke(Object[] args)
                       throws XPathEvaluationException

Invoke the function using the passed list of arguments. This member uses introspection to perform the invocation; better performance can be obtained by overriding this member in derived classes. This member MUST be overridden for those function implementations that accept differing argument types.

Parameters:

args - List of arguments.

Returns:

An object containing the result of the function invocation.

Throws:

XPathEvaluationException

isConstant

public boolean isConstant()

Return true if the expression is a constant value. Default return is false. Derived functions may want to override this (true(), false(), for example)

Returns:

True is expression is constant, false otherwise.

registerForReset

public void registerForReset(XPathResetRegistrar registrar)

Register this expression or any subexpression that implements XPathResetCache with an object that wants to call resetCache()

getSignature

protected FunctionSignature getSignature()

Return the signature for this Function.

Returns:

The object describing the function signature.