View Javadoc
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  }