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.apache.reef.tang.util.walk;
020
021import org.apache.reef.tang.types.Traversable;
022
023/**
024 * Generic graph traversal.
025 */
026public final class Walk {
027
028  /**
029   * This is a utility class that has only static methods - do not instantiate.
030   *
031   * @throws IllegalAccessException always.
032   */
033  private Walk() throws IllegalAccessException {
034    throw new IllegalAccessException("Do not instantiate this class.");
035  }
036
037  /**
038   * Traverse the configuration (sub)tree in preorder, starting from the given node.
039   * FIXME: handle loopy graphs correctly!
040   *
041   * @param nodeVisitor node visitor. Can be null.
042   * @param edgeVisitor edge visitor. Can be null.
043   * @param node        current node of the configuration tree.
044   * @return true if all nodes has been walked, false if visitor stopped early.
045   */
046  public static <T extends Traversable<T>> boolean preorder(
047      final NodeVisitor<T> nodeVisitor, final EdgeVisitor<T> edgeVisitor, final T node) {
048    if (nodeVisitor != null && nodeVisitor.visit(node)) {
049      if (edgeVisitor != null) {
050        for (final T child : node.getChildren()) {
051          if (!(edgeVisitor.visit(node, child)
052              && preorder(nodeVisitor, edgeVisitor, child))) {
053            return false;
054          }
055        }
056      } else {
057        for (final T child : node.getChildren()) {
058          if (!preorder(nodeVisitor, null, child)) {
059            return false;
060          }
061        }
062      }
063    }
064    return true;
065  }
066}