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package org.apache.cayenne.exp;

/**
 * Expression visitor interface. Defines callback methods invoked when 
 * walking the expression using {@link Expression#traverse(TraversalHandler)}.
 * 
 * @author Andrei Adamchik
 */
public interface TraversalHandler {

    /** 
     * Called during traversal after a child of expression
     * has been visited. 
     */
    public void finishedChild(
        Expression node,
        int childIndex,
        boolean hasMoreChildren);
  
    /** 
     * Called during the traversal before an expression node children
     * processing is started.
     * 
     * @since 1.1
     */
    public void startNode(Expression node, Expression parentNode);
    
    /** 
     * Called during the traversal after an expression node children
     * processing is finished.
     * 
     * @since 1.1
     */
    public void endNode(Expression node, Expression parentNode);
    
    /** 
     * Called during the traversal when a leaf non-expression node 
     * is encountered.
     */
    public void objectNode(Object leaf, Expression parentNode);
}
