1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one
3 * or more contributor license agreements. See the NOTICE file
4 * distributed with this work for additional information
5 * regarding copyright ownership. The ASF licenses this file
6 * to you under the Apache License, Version 2.0 (the
7 * "License"); you may not use this file except in compliance
8 * with the License. You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing,
13 * software distributed under the License is distributed on an
14 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15 * KIND, either express or implied. See the License for the
16 * specific language governing permissions and limitations
17 * under the License.
18 */
19 package org.eclipse.aether.util.graph.visitor;
20
21 import org.eclipse.aether.graph.DependencyNode;
22
23 /**
24 * Generates a sequence of dependency nodes from a dependency graph by traversing the graph in postorder. This visitor
25 * visits each node exactly once regardless how many paths within the dependency graph lead to the node such that the
26 * resulting node sequence is free of duplicates.
27 * <p>
28 * The newer classes {@link AbstractDependencyNodeConsumerVisitor} and {@link NodeListGenerator} offer
29 * similar capabilities but are pluggable. Use of this class, while not deprecated, is discouraged. This class
30 * is not used in Resolver and is kept only for backward compatibility reasons.
31 *
32 * @see PostorderDependencyNodeConsumerVisitor
33 * @see NodeListGenerator
34 */
35 public final class PostorderNodeListGenerator extends AbstractDepthFirstNodeListGenerator {
36
37 private final Stack<Boolean> visits;
38
39 /**
40 * Creates a new postorder list generator.
41 */
42 public PostorderNodeListGenerator() {
43 visits = new Stack<>();
44 }
45
46 @Override
47 public boolean visitEnter(DependencyNode node) {
48 boolean visited = !setVisited(node);
49
50 visits.push(visited);
51
52 return !visited;
53 }
54
55 @Override
56 public boolean visitLeave(DependencyNode node) {
57 Boolean visited = visits.pop();
58
59 if (visited) {
60 return true;
61 }
62
63 if (node.getDependency() != null) {
64 nodes.add(node);
65 }
66
67 return true;
68 }
69 }