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.operations;
  
  import org.apache.xpath.Expression;
  import org.apache.xpath.ExpressionOwner;
  import org.apache.xpath.XPathContext;
  import org.apache.xpath.XPathVisitor;
  import org.apache.xpath.objects.XObject;
  
  /**
   * The baseclass for a binary operation.
   */
  public class Operation extends Expression implements ExpressionOwner
  {
      static final long serialVersionUID = -3037139537171050430L;
  
    /** The left operand expression.
     *  @serial */
    protected Expression m_left;
  
    /** The right operand expression.
     *  @serial */
    protected Expression m_right;
    
    /**
     * This function is used to fixup variables from QNames to stack frame 
     * indexes at stylesheet build time.
     * @param vars List of QNames that correspond to variables.  This list 
     * should be searched backwards for the first qualified name that 
     * corresponds to the variable reference qname.  The position of the 
     * QName in the vector from the start of the vector will be its position 
     * in the stack frame (but variables above the globalsTop value will need 
     * to be offset to the current stack frame).
     */
    public void fixupVariables(java.util.Vector vars, int globalsSize)
    {
      m_left.fixupVariables(vars, globalsSize);
      m_right.fixupVariables(vars, globalsSize);
    }
  
  
    /**
     * Tell if this expression or it's subexpressions can traverse outside
     * the current subtree.
     *
     * @return true if traversal outside the context node's subtree can occur.
     */
    public boolean canTraverseOutsideSubtree()
    {
  
      if (null != m_left && m_left.canTraverseOutsideSubtree())
        return true;
  
      if (null != m_right && m_right.canTraverseOutsideSubtree())
        return true;
  
      return false;
    }
  
    /**
     * Set the left and right operand expressions for this operation.
     *
     *
     * @param l The left expression operand.
     * @param r The right expression operand.
     */
    public void setLeftRight(Expression l, Expression r)
    {
      m_left = l;
      m_right = r;
      l.exprSetParent(this);
      r.exprSetParent(this);
    }
  
    /**
     * Execute a binary operation by calling execute on each of the operands,
     * and then calling the operate method on the derived class.
     *
     *
     * @param xctxt The runtime execution context.
     *
     * @return The XObject result of the operation.
     *
     * @throws javax.xml.transform.TransformerException
     */
    public XObject execute(XPathContext xctxt)
            throws javax.xml.transform.TransformerException
    {
  
      XObject left = m_left.execute(xctxt, true);
      XObject right = m_right.execute(xctxt, true);
  
      XObject result = operate(left, right);
      left.detach();
      right.detach();
      return result;
    }
  
    /**
     * Apply the operation to two operands, and return the result.
     *
     *
     * @param left non-null reference to the evaluated left operand.
     * @param right non-null reference to the evaluated right operand.
     *
     * @return non-null reference to the XObject that represents the result of the operation.
     *
     * @throws javax.xml.transform.TransformerException
     */
    public XObject operate(XObject left, XObject right)
            throws javax.xml.transform.TransformerException
    {
      return null;  // no-op
    }
  
    /** @return the left operand of binary operation, as an Expression.
     */
    public Expression getLeftOperand(){
      return m_left;
    }
  
    /** @return the right operand of binary operation, as an Expression.
     */
    public Expression getRightOperand(){
      return m_right;
    }
    
    class LeftExprOwner implements ExpressionOwner
    {
      /**
       * @see ExpressionOwner#getExpression()
       */
      public Expression getExpression()
      {
        return m_left;
      }
  
      /**
       * @see ExpressionOwner#setExpression(Expression)
       */
      public void setExpression(Expression exp)
      {
      	exp.exprSetParent(Operation.this);
      	m_left = exp;
      }
    }
  
    /**
     * @see org.apache.xpath.XPathVisitable#callVisitors(ExpressionOwner, XPathVisitor)
     */
    public void callVisitors(ExpressionOwner owner, XPathVisitor visitor)
    {
    	if(visitor.visitBinaryOperation(owner, this))
    	{
    		m_left.callVisitors(new LeftExprOwner(), visitor);
    		m_right.callVisitors(this, visitor);
    	}
    }
  
    /**
     * @see ExpressionOwner#getExpression()
     */
    public Expression getExpression()
    {
      return m_right;
    }
  
    /**
     * @see ExpressionOwner#setExpression(Expression)
     */
    public void setExpression(Expression exp)
    {
    	exp.exprSetParent(this);
    	m_right = exp;
    }
  
    /**
     * @see Expression#deepEquals(Expression)
     */
    public boolean deepEquals(Expression expr)
    {
    	if(!isSameClass(expr))
    		return false;
    		
    	if(!m_left.deepEquals(((Operation)expr).m_left))
    		return false;
    		
    	if(!m_right.deepEquals(((Operation)expr).m_right))
    		return false;
    		
    	return true;
    }
  }
  