001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *   http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing,
013 * software distributed under the License is distributed on an
014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 * KIND, either express or implied.  See the License for the
016 * specific language governing permissions and limitations
017 * under the License.
018 */
019package org.eclipse.aether.util.graph.visitor;
020
021import org.eclipse.aether.graph.DependencyNode;
022
023/**
024 * Generates a sequence of dependency nodes from a dependency graph by traversing the graph in preorder. This visitor
025 * visits each node exactly once regardless how many paths within the dependency graph lead to the node such that the
026 * resulting node sequence is free of duplicates.
027 * <p>
028 * The newer classes {@link AbstractDependencyNodeConsumerVisitor} and {@link NodeListGenerator} offer
029 * similar capabilities but are pluggable. Use of this class, while not deprecated, is discouraged. This class
030 * is not used in Resolver and is kept only for backward compatibility reasons.
031 *
032 * @see PreorderDependencyNodeConsumerVisitor
033 * @see NodeListGenerator
034 */
035public final class PreorderNodeListGenerator extends AbstractDepthFirstNodeListGenerator {
036
037    /**
038     * Creates a new preorder list generator.
039     */
040    public PreorderNodeListGenerator() {}
041
042    @Override
043    public boolean visitEnter(DependencyNode node) {
044        if (!setVisited(node)) {
045            return false;
046        }
047
048        if (node.getDependency() != null) {
049            nodes.add(node);
050        }
051
052        return true;
053    }
054
055    @Override
056    public boolean visitLeave(DependencyNode node) {
057        return true;
058    }
059}