src/main/java/org/apache/commons/ognl/Node.java

package org.apache.commons.ognl;

/*
 * 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.
 */

import org.apache.commons.ognl.enhance.ExpressionAccessor;

/**
 * JJTree interface for AST nodes, as modified to handle the OGNL operations getValue and setValue. JJTree's original
 * comment: All AST nodes must implement this interface. It provides basic machinery for constructing the parent and
 * child relationships between nodes.
 */
public interface Node
    extends JavaSource
{

    /**
     * This method is called after the node has been made the current node. It indicates that child nodes can now be
     * added to it.
     */
    void jjtOpen();

    /**
     * This method is called after all the child nodes have been added.
     */
    void jjtClose();

    /**
     * This pair of methods are used to inform the node of its parent.
     */
    void jjtSetParent( Node n );

    Node jjtGetParent();

    /**
     * This method tells the node to add its argument to the node's list of children.
     */
    void jjtAddChild( Node n, int i );

    /**
     * This method returns a child node. The children are numbered from zero, left to right.
     */
    Node jjtGetChild( int i );

    /** Return the number of children the node has. */
    int jjtGetNumChildren();

    // OGNL additions to Node:

    /**
     * Extracts the value from the given source object that is appropriate for this node within the given context.
     */
    Object getValue( OgnlContext context, Object source )
        throws OgnlException;

    /**
     * Sets the given value in the given target as appropriate for this node within the given context.
     */
    void setValue( OgnlContext context, Object target, Object value )
        throws OgnlException;

    /**
     * Gets the compiled bytecode enhanced expression accessor for getting/setting values.
     *
     * @return The accessor for this node, or null if none has been compiled for it.
     */
    ExpressionAccessor getAccessor();

    /**
     * Sets a new compiled accessor for this node expression.
     *
     * @param accessor The compiled representation of this node.
     */
    void setAccessor( ExpressionAccessor accessor );


    /**
     * Supports the Visitor pattern. The method which corresponds to
     * the runtime type of this Node will be called.
     *
     * @param visitor The visitor to accept.
     * @param data    The second parameter to pass through to visitor.visit
     * @param <R>     The return type of the visitor.visit method.
     * @param <P>     The type of the second parameter type.
     * @return the value returned by visitor.visit
     * @throws NullPointerException if visitor is null
     * @throws RuntimeException     if visitor.visit throws an exception.
     */
    <R, P> R accept( NodeVisitor<? extends R, ? super P> visitor, P data )
        throws OgnlException;

}