http://xml.apache.org/xalan-j/: Serializer to write out XML, HTML etc. as a stream of characters from an input DOM or from input SAX events. (The Apache Software Foundation) 
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 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the  "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
/*
 * $Id: Function.java 468655 2006-10-28 07:12:06Z minchau $
 */
package org.apache.xpath.functions;

import org.apache.xalan.res.XSLMessages;
import org.apache.xpath.Expression;
import org.apache.xpath.ExpressionOwner;
import org.apache.xpath.XPathContext;
import org.apache.xpath.XPathVisitor;
import org.apache.xpath.compiler.Compiler;
import org.apache.xpath.objects.XObject;


This is a superclass of all XPath functions.  This allows two
ways for the class to be called. One method is that the
super class processes the arguments and hands the results to
the derived class, the other method is that the derived
class may process it's own arguments, which is faster since
the arguments don't have to be added to an array, but causes
a larger code footprint.

@xsl.usageadvanced
/**
 * This is a superclass of all XPath functions.  This allows two
 * ways for the class to be called. One method is that the
 * super class processes the arguments and hands the results to
 * the derived class, the other method is that the derived
 * class may process it's own arguments, which is faster since
 * the arguments don't have to be added to an array, but causes
 * a larger code footprint.
 * @xsl.usage advanced
 */
public abstract class Function extends Expression
{
    static final long serialVersionUID = 6927661240854599768L;

  
Set an argument expression for a function.  This method is called by the 
XPath compiler.

Params:
  • arg – non-null expression that represents the argument.
  • argNum – The argument number index.
Throws:
/**
   * Set an argument expression for a function.  This method is called by the 
   * XPath compiler.
   *
   * @param arg non-null expression that represents the argument.
   * @param argNum The argument number index.
   *
   * @throws WrongNumberArgsException If the argNum parameter is beyond what 
   * is specified for this function.
   */
  public void setArg(Expression arg, int argNum)
          throws WrongNumberArgsException
  {
			// throw new WrongNumberArgsException(XSLMessages.createXPATHMessage("zero", null));
      reportWrongNumberArgs();
  }

  
Check that the number of arguments passed to this function is correct.
This method is meant to be overloaded by derived classes, to check for 
the number of arguments for a specific function type.  This method is 
called by the compiler for static number of arguments checking.

Params:
  • argNum – The number of arguments that is being passed to the function.
Throws:
/**
   * Check that the number of arguments passed to this function is correct.
   * This method is meant to be overloaded by derived classes, to check for 
   * the number of arguments for a specific function type.  This method is 
   * called by the compiler for static number of arguments checking.
   *
   * @param argNum The number of arguments that is being passed to the function.
   *
   * @throws WrongNumberArgsException
   */
  public void checkNumberArgs(int argNum) throws WrongNumberArgsException
  {
    if (argNum != 0)
      reportWrongNumberArgs();
  }

  
Constructs and throws a WrongNumberArgException with the appropriate
message for this function object.  This method is meant to be overloaded
by derived classes so that the message will be as specific as possible.

Throws:
  • WrongNumberArgsException – 
/**
   * Constructs and throws a WrongNumberArgException with the appropriate
   * message for this function object.  This method is meant to be overloaded
   * by derived classes so that the message will be as specific as possible.
   *
   * @throws WrongNumberArgsException
   */
  protected void reportWrongNumberArgs() throws WrongNumberArgsException {
      throw new WrongNumberArgsException(XSLMessages.createXPATHMessage("zero", null));
  }

  
Execute an XPath function object.  The function must return
a valid object.

Params:
  • xctxt – The execution current context.
Throws:
Returns:A valid XObject.
/**
   * Execute an XPath function object.  The function must return
   * a valid object.
   * @param xctxt The execution current context.
   * @return A valid XObject.
   *
   * @throws javax.xml.transform.TransformerException
   */
  public XObject execute(XPathContext xctxt) throws javax.xml.transform.TransformerException
  {

    // Programmer's assert.  (And, no, I don't want the method to be abstract).
    System.out.println("Error! Function.execute should not be called!");

    return null;
  }
  
  
Call the visitors for the function arguments.

/**
   * Call the visitors for the function arguments.
   */
  public void callArgVisitors(XPathVisitor visitor)
  {
  }

  
  
See Also:
  • callVisitors.callVisitors(ExpressionOwner, XPathVisitor)
/**
   * @see org.apache.xpath.XPathVisitable#callVisitors(ExpressionOwner, XPathVisitor)
   */
  public void callVisitors(ExpressionOwner owner, XPathVisitor visitor)
  {
  	if(visitor.visitFunction(owner, this))
  	{
  		callArgVisitors(visitor);
  	}
  }
  
  
See Also:
  • deepEquals.deepEquals(Expression)
/**
   * @see Expression#deepEquals(Expression)
   */
  public boolean deepEquals(Expression expr)
  {
  	if(!isSameClass(expr))
  		return false;
  		
  	return true;
  }

  
This function is currently only being used by Position()
and Last(). See respective functions for more detail.

/**
   * This function is currently only being used by Position()
   * and Last(). See respective functions for more detail.
   */
  public void postCompileStep(Compiler compiler)
  {
    // no default action
  }
}