001package org.eclipse.aether.util.graph.visitor; 002 003/* 004 * Licensed to the Apache Software Foundation (ASF) under one 005 * or more contributor license agreements. See the NOTICE file 006 * distributed with this work for additional information 007 * regarding copyright ownership. The ASF licenses this file 008 * to you under the Apache License, Version 2.0 (the 009 * "License"); you may not use this file except in compliance 010 * with the License. You may obtain a copy of the License at 011 * 012 * http://www.apache.org/licenses/LICENSE-2.0 013 * 014 * Unless required by applicable law or agreed to in writing, 015 * software distributed under the License is distributed on an 016 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY 017 * KIND, either express or implied. See the License for the 018 * specific language governing permissions and limitations 019 * under the License. 020 */ 021 022import org.eclipse.aether.graph.DependencyNode; 023 024/** 025 * Generates a sequence of dependency nodes from a dependeny graph by traversing the graph in postorder. This visitor 026 * visits each node exactly once regardless how many paths within the dependency graph lead to the node such that the 027 * resulting node sequence is free of duplicates. 028 */ 029public final class PostorderNodeListGenerator 030 extends AbstractDepthFirstNodeListGenerator 031{ 032 033 private final Stack<Boolean> visits; 034 035 /** 036 * Creates a new postorder list generator. 037 */ 038 public PostorderNodeListGenerator() 039 { 040 visits = new Stack<>(); 041 } 042 043 @Override 044 public boolean visitEnter( DependencyNode node ) 045 { 046 boolean visited = !setVisited( node ); 047 048 visits.push( visited ); 049 050 if ( visited ) 051 { 052 return false; 053 } 054 055 return true; 056 } 057 058 @Override 059 public boolean visitLeave( DependencyNode node ) 060 { 061 Boolean visited = visits.pop(); 062 063 if ( visited ) 064 { 065 return true; 066 } 067 068 if ( node.getDependency() != null ) 069 { 070 nodes.add( node ); 071 } 072 073 return true; 074 } 075 076}