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 preorder. 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 PreorderNodeListGenerator
030    extends AbstractDepthFirstNodeListGenerator
031{
032
033    /**
034     * Creates a new preorder list generator.
035     */
036    public PreorderNodeListGenerator()
037    {
038    }
039
040    @Override
041    public boolean visitEnter( DependencyNode node )
042    {
043        if ( !setVisited( node ) )
044        {
045            return false;
046        }
047
048        if ( node.getDependency() != null )
049        {
050            nodes.add( node );
051        }
052
053        return true;
054    }
055
056    @Override
057    public boolean visitLeave( DependencyNode node )
058    {
059        return true;
060    }
061
062}