Function.java revision 9f8118474e9513f7a5b7d2a05e4a0fb15d1a6569 
1/*
2 * Licensed to the Apache Software Foundation (ASF) under one
3 * or more contributor license agreements. See the NOTICE file
4 * distributed with this work for additional information
5 * regarding copyright ownership. The ASF licenses this file
6 * to you under the Apache License, Version 2.0 (the  "License");
7 * you may not use this file except in compliance with the License.
8 * You may obtain a copy of the License at
9 *
10 *     http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing, software
13 * distributed under the License is distributed on an "AS IS" BASIS,
14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15 * See the License for the specific language governing permissions and
16 * limitations under the License.
17 */
18/*
19 * $Id: Function.java 468655 2006-10-28 07:12:06Z minchau $
20 */
21package org.apache.xpath.functions;
22
23import org.apache.xalan.res.XSLMessages;
24import org.apache.xpath.Expression;
25import org.apache.xpath.ExpressionOwner;
26import org.apache.xpath.XPathContext;
27import org.apache.xpath.XPathVisitor;
28import org.apache.xpath.compiler.Compiler;
29import org.apache.xpath.objects.XObject;
30
31/**
32 * This is a superclass of all XPath functions.  This allows two
33 * ways for the class to be called. One method is that the
34 * super class processes the arguments and hands the results to
35 * the derived class, the other method is that the derived
36 * class may process it's own arguments, which is faster since
37 * the arguments don't have to be added to an array, but causes
38 * a larger code footprint.
39 * @xsl.usage advanced
40 */
41public abstract class Function extends Expression
42{
43    static final long serialVersionUID = 6927661240854599768L;
44
45  /**
46   * Set an argument expression for a function.  This method is called by the
47   * XPath compiler.
48   *
49   * @param arg non-null expression that represents the argument.
50   * @param argNum The argument number index.
51   *
52   * @throws WrongNumberArgsException If the argNum parameter is beyond what
53   * is specified for this function.
54   */
55  public void setArg(Expression arg, int argNum)
56          throws WrongNumberArgsException
57  {
58			// throw new WrongNumberArgsException(XSLMessages.createXPATHMessage("zero", null));
59      reportWrongNumberArgs();
60  }
61
62  /**
63   * Check that the number of arguments passed to this function is correct.
64   * This method is meant to be overloaded by derived classes, to check for
65   * the number of arguments for a specific function type.  This method is
66   * called by the compiler for static number of arguments checking.
67   *
68   * @param argNum The number of arguments that is being passed to the function.
69   *
70   * @throws WrongNumberArgsException
71   */
72  public void checkNumberArgs(int argNum) throws WrongNumberArgsException
73  {
74    if (argNum != 0)
75      reportWrongNumberArgs();
76  }
77
78  /**
79   * Constructs and throws a WrongNumberArgException with the appropriate
80   * message for this function object.  This method is meant to be overloaded
81   * by derived classes so that the message will be as specific as possible.
82   *
83   * @throws WrongNumberArgsException
84   */
85  protected void reportWrongNumberArgs() throws WrongNumberArgsException {
86      throw new WrongNumberArgsException(XSLMessages.createXPATHMessage("zero", null));
87  }
88
89  /**
90   * Execute an XPath function object.  The function must return
91   * a valid object.
92   * @param xctxt The execution current context.
93   * @return A valid XObject.
94   *
95   * @throws javax.xml.transform.TransformerException
96   */
97  public XObject execute(XPathContext xctxt) throws javax.xml.transform.TransformerException
98  {
99
100    // Programmer's assert.  (And, no, I don't want the method to be abstract).
101    System.out.println("Error! Function.execute should not be called!");
102
103    return null;
104  }
105
106  /**
107   * Call the visitors for the function arguments.
108   */
109  public void callArgVisitors(XPathVisitor visitor)
110  {
111  }
112
113
114  /**
115   * @see org.apache.xpath.XPathVisitable#callVisitors(ExpressionOwner, XPathVisitor)
116   */
117  public void callVisitors(ExpressionOwner owner, XPathVisitor visitor)
118  {
119  	if(visitor.visitFunction(owner, this))
120  	{
121  		callArgVisitors(visitor);
122  	}
123  }
124
125  /**
126   * @see Expression#deepEquals(Expression)
127   */
128  public boolean deepEquals(Expression expr)
129  {
130  	if(!isSameClass(expr))
131  		return false;
132
133  	return true;
134  }
135
136  /**
137   * This function is currently only being used by Position()
138   * and Last(). See respective functions for more detail.
139   */
140  public void postCompileStep(Compiler compiler)
141  {
142    // no default action
143  }
144}
145