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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 dependeny 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   */
28  public final class PostorderNodeListGenerator extends AbstractDepthFirstNodeListGenerator {
29  
30      private final Stack<Boolean> visits;
31  
32      /**
33       * Creates a new postorder list generator.
34       */
35      public PostorderNodeListGenerator() {
36          visits = new Stack<>();
37      }
38  
39      @Override
40      public boolean visitEnter(DependencyNode node) {
41          boolean visited = !setVisited(node);
42  
43          visits.push(visited);
44  
45          return !visited;
46      }
47  
48      @Override
49      public boolean visitLeave(DependencyNode node) {
50          Boolean visited = visits.pop();
51  
52          if (visited) {
53              return true;
54          }
55  
56          if (node.getDependency() != null) {
57              nodes.add(node);
58          }
59  
60          return true;
61      }
62  }