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;
  
  import org.apache.xpath.axes.LocPathIterator;
  import org.apache.xpath.axes.UnionPathIterator;
  import org.apache.xpath.functions.Function;
  import org.apache.xpath.objects.XNumber;
  import org.apache.xpath.objects.XString;
  import org.apache.xpath.operations.Operation;
  import org.apache.xpath.operations.UnaryOperation;
  import org.apache.xpath.operations.Variable;
  import org.apache.xpath.patterns.NodeTest;
  import org.apache.xpath.patterns.StepPattern;
  import org.apache.xpath.patterns.UnionPattern;
  
  /**
   * A derivation from this class can be passed to a class that implements 
   * the XPathVisitable interface, to have the appropriate method called 
   * for each component of the XPath.  Aside from possible other uses, the 
   * main intention is to provide a reasonable means to perform expression 
   * rewriting.
   * 
   * <p>Each method has the form 
   * <code>boolean visitComponentType(ExpressionOwner owner, ComponentType compType)</code>. 
   * The ExpressionOwner argument is the owner of the component, and can 
   * be used to reset the expression for rewriting.  If a method returns 
   * false, the sub hierarchy will not be traversed.</p>
   * 
   * <p>This class is meant to be a base class that will be derived by concrete classes, 
   * and doesn't much except return true for each method.</p>
   */
  public class XPathVisitor
  {
  	/**
  	 * Visit a LocationPath.
  	 * @param owner The owner of the expression, to which the expression can 
  	 *              be reset if rewriting takes place.
  	 * @param path The LocationPath object.
  	 * @return true if the sub expressions should be traversed.
  	 */
  	public boolean visitLocationPath(ExpressionOwner owner, LocPathIterator path)
  	{
  		return true;
  	}
  
  	/**
  	 * Visit a UnionPath.
  	 * @param owner The owner of the expression, to which the expression can 
  	 *              be reset if rewriting takes place.
  	 * @param path The UnionPath object.
  	 * @return true if the sub expressions should be traversed.
  	 */
  	public boolean visitUnionPath(ExpressionOwner owner, UnionPathIterator path)
  	{
  		return true;
  	}
  	
  	/**
  	 * Visit a step within a location path.
  	 * @param owner The owner of the expression, to which the expression can 
  	 *              be reset if rewriting takes place.
  	 * @param step The Step object.
  	 * @return true if the sub expressions should be traversed.
  	 */
  	public boolean visitStep(ExpressionOwner owner, NodeTest step)
  	{
  		return true;
  	}
  		
  	/**
  	 * Visit a predicate within a location path.  Note that there isn't a 
  	 * proper unique component for predicates, and that the expression will 
  	 * be called also for whatever type Expression is.
  	 * 
  	 * @param owner The owner of the expression, to which the expression can 
  	 *              be reset if rewriting takes place.
  	 * @param pred The predicate object.
  	 * @return true if the sub expressions should be traversed.
  	 */
  	public boolean visitPredicate(ExpressionOwner owner, Expression pred)
  	{
  		return true;
  	}
  
  	/**
  	 * Visit a binary operation.
  	 * @param owner The owner of the expression, to which the expression can 
  	 *              be reset if rewriting takes place.
  	 * @param op The operation object.
  	 * @return true if the sub expressions should be traversed.
  	 */
  	public boolean visitBinaryOperation(ExpressionOwner owner, Operation op)
  	{
  		return true;
  	}
  
  	/**
  	 * Visit a unary operation.
  	 * @param owner The owner of the expression, to which the expression can 
  	 *              be reset if rewriting takes place.
  	 * @param op The operation object.
  	 * @return true if the sub expressions should be traversed.
  	 */
  	public boolean visitUnaryOperation(ExpressionOwner owner, UnaryOperation op)
  	{
  		return true;
  	}
  	
  	/**
  	 * Visit a variable reference.
  	 * @param owner The owner of the expression, to which the expression can 
  	 *              be reset if rewriting takes place.
  	 * @param var The variable reference object.
  	 * @return true if the sub expressions should be traversed.
  	 */
  	public boolean visitVariableRef(ExpressionOwner owner, Variable var)
  	{
  		return true;
  	}
  
  	/**
  	 * Visit a function.
  	 * @param owner The owner of the expression, to which the expression can 
  	 *              be reset if rewriting takes place.
  	 * @param func The function reference object.
  	 * @return true if the sub expressions should be traversed.
  	 */
  	public boolean visitFunction(ExpressionOwner owner, Function func)
  	{
  		return true;
  	}
  	
  	/**
  	 * Visit a match pattern.
  	 * @param owner The owner of the expression, to which the expression can 
  	 *              be reset if rewriting takes place.
  	 * @param pattern The match pattern object.
  	 * @return true if the sub expressions should be traversed.
  	 */
  	public boolean visitMatchPattern(ExpressionOwner owner, StepPattern pattern)
  	{
  		return true;
  	}
  	
  	/**
  	 * Visit a union pattern.
  	 * @param owner The owner of the expression, to which the expression can 
  	 *              be reset if rewriting takes place.
  	 * @param pattern The union pattern object.
  	 * @return true if the sub expressions should be traversed.
  	 */
  	public boolean visitUnionPattern(ExpressionOwner owner, UnionPattern pattern)
  	{
  		return true;
  	}
  	
  	/**
  	 * Visit a string literal.
  	 * @param owner The owner of the expression, to which the expression can 
  	 *              be reset if rewriting takes place.
  	 * @param str The string literal object.
  	 * @return true if the sub expressions should be traversed.
  	 */
  	public boolean visitStringLiteral(ExpressionOwner owner, XString str)
  	{
  		return true;
  	}
  
  
  	/**
  	 * Visit a number literal.
  	 * @param owner The owner of the expression, to which the expression can 
  	 *              be reset if rewriting takes place.
  	 * @param num The number literal object.
  	 * @return true if the sub expressions should be traversed.
  	 */
  	public boolean visitNumberLiteral(ExpressionOwner owner, XNumber num)
  	{
  		return true;
  	}
  
  
  }
  
  