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
015package 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 */
024public 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}