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 }