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 java.util.function.Consumer;
22
23 import org.eclipse.aether.graph.DependencyNode;
24
25 /**
26 * Processes dependency graph by traversing the graph in postorder. This visitor visits each node exactly once
27 * regardless how many paths within the dependency graph lead to the node such that the resulting node sequence is
28 * free of duplicates.
29 *
30 * @since TBD
31 */
32 public final class PostorderDependencyNodeConsumerVisitor extends AbstractDependencyNodeConsumerVisitor {
33
34 public static final String NAME = "postOrder";
35
36 private final Stack<Boolean> visits;
37
38 /**
39 * Creates a new postorder list generator.
40 */
41 public PostorderDependencyNodeConsumerVisitor(Consumer<DependencyNode> nodeConsumer) {
42 super(nodeConsumer);
43 visits = new Stack<>();
44 }
45
46 @Override
47 public boolean visitEnter(DependencyNode node) {
48 boolean visited = !setVisited(node);
49 visits.push(visited);
50 return !visited;
51 }
52
53 @Override
54 public boolean visitLeave(DependencyNode node) {
55 Boolean visited = visits.pop();
56 if (visited) {
57 return true;
58 }
59 nodeConsumer.accept(node);
60 return true;
61 }
62 }