// Copyright 2014 The Bazel Authors. All rights reserved.
//
// Licensed 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.
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package com.google.devtools.build.lib.graph;
/**
* <p> An graph visitor interface; particularly useful for allowing subclasses
* to specify how to output a graph. The order in which node and edge
* callbacks are made (DFS, BFS, etc) is defined by the choice of Digraph
* visitation method used. </p>
*/
public interface GraphVisitor<T> {
/**
* Called before visitation commences.
*/
void beginVisit();
/**
* Called after visitation is complete.
*/
void endVisit();
/**
* <p> Called for each edge. </p>
*
* TODO(bazel-team): This method is not essential, and in all known cases so
* far, the visitEdge code can always be placed within visitNode. Perhaps
* we should remove it, and the begin/end methods, and make this just a
* NodeVisitor? Are there any algorithms for which edge-visitation order is
* important?
*/
void visitEdge(Node<T> lhs, Node<T> rhs);
/**
* Called for each node.
*/
void visitNode(Node<T> node);
}