001    // Copyright 2004, 2005 The Apache Software Foundation
002    //
003    // Licensed under the Apache License, Version 2.0 (the "License");
004    // you may not use this file except in compliance with the License.
005    // You may obtain a copy of the License at
006    //
007    //     http://www.apache.org/licenses/LICENSE-2.0
008    //
009    // Unless required by applicable law or agreed to in writing, software
010    // distributed under the License is distributed on an "AS IS" BASIS,
011    // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012    // See the License for the specific language governing permissions and
013    // limitations under the License.
014    
015    package org.apache.hivemind.conditional;
016    
017    /**
018     * An evaluator is paired with a {@link Node}. The Node provides structure, the Evaluator provides
019     * meaning, interpreting the node.
020     * 
021     * @author Howard M. Lewis Ship
022     * @since 1.1
023     */
024    public interface Evaluator
025    {
026        /**
027         * Invoked by the Node to evaluate its own value. Typical implementations will extract the
028         * Node's {@link org.apache.hivemind.conditional.Node#getLeft() left} and
029         * {@link org.apache.hivemind.conditional.Node#getRight() right} properties and combine or
030         * otherwise evaluate them. Terminal nodes in the tree will have evaluators that don't do that
031         * but generate a return value internally.
032         */
033    
034        public boolean evaluate(EvaluationContext context, Node node);
035    }