code: /*
   * 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.
   */
  /*
   * $Id$
   */
  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.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.
     *
     * @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.
     *
     * @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
     */
    protected void reportWrongNumberArgs() throws WrongNumberArgsException {
        throw new WrongNumberArgsException(XSLMessages.createXPATHMessage("zero", null));
    }
  
    /**
     * 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.
     */
    public void callArgVisitors(XPathVisitor visitor)
    {
    }
  
    
    /**
     * @see org.apache.xpath.XPathVisitable#callVisitors(ExpressionOwner, XPathVisitor)
     */
    public void callVisitors(ExpressionOwner owner, XPathVisitor visitor)
    {
    	if(visitor.visitFunction(owner, this))
    	{
    		callArgVisitors(visitor);
    	}
    }
    
    /**
     * @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.
     */
    public void postCompileStep(Compiler compiler)
    {
      // no default action
    }
  }
  