@ElementTypesAreNonnullByDefault
public abstract class Traverser<N> {
  private final SuccessorsFunction<N> successorFunction;

  private Traverser(SuccessorsFunction<N> successorFunction) {
    this.successorFunction = checkNotNull(successorFunction);
  }

  /**
   * Creates a new traverser for the given general {@code graph}.
   *
   * <p>Traversers created using this method are guaranteed to visit each node reachable from the

@ElementTypesAreNonnullByDefault
public abstract class Traverser<N> {
  private final SuccessorsFunction<N> successorFunction;

  private Traverser(SuccessorsFunction<N> successorFunction) {
    this.successorFunction = checkNotNull(successorFunction);
  }

  /**
   * Creates a new traverser for the given general {@code graph}.
   *
   * <p>Traversers created using this method are guaranteed to visit each node reachable from the

 * @see URLUtil#toCanonicalProtocol(String)
 * @see ClassTraversalUtil
 * @see ResourceTraversalUtil
 */
public abstract class TraversalUtil {

    /** 空の{@link Traverser}の配列です。 */
    protected static final Traverser[] EMPTY_ARRAY = new Traverser[0];

    private static final Logger logger = Logger.getLogger(TraversalUtil.class);

    /** URLのプロトコルをキー、{@link TraverserFactory}を値とするマッピングです。 */

    assertEqualCharNodes(traverser.breadthFirst(charactersOf("acdb")), "acdb");
    assertEqualCharNodes(traverser.breadthFirst(charactersOf("db")), "db");
  }

  @Test
  public void forGraph_breadthFirst_multiGraph() {
    Traverser<Character> traverser = Traverser.forGraph(MULTI_GRAPH);
    assertEqualCharNodes(traverser.breadthFirst('a'), "abcd");

    assertEqualCharNodes(traverser.breadthFirst(charactersOf("acdb")), "acdb");
    assertEqualCharNodes(traverser.breadthFirst(charactersOf("db")), "db");
  }

  @Test
  public void forGraph_breadthFirst_multiGraph() {
    Traverser<Character> traverser = Traverser.forGraph(MULTI_GRAPH);
    assertEqualCharNodes(traverser.breadthFirst('a'), "abcd");

      throw e.getCause();
    }
  }

  /**
   * Returns a {@link Traverser} instance for the file and directory tree. The returned traverser
   * starts from a {@link Path} and will return all files and directories it encounters.
   *
   * <p>The returned traverser attempts to avoid following symbolic links to directories. However,
   * the traverser cannot guarantee that it will not follow symbolic links to directories as it is

    int dotIndex = fileName.lastIndexOf('.');
    return (dotIndex == -1) ? fileName : fileName.substring(0, dotIndex);
  }

  /**
   * Returns a {@link Traverser} instance for the file and directory tree. The returned traverser
   * starts from a {@link File} and will return all files and directories it encounters.
   *
   * <p><b>Warning:</b> {@code File} provides no support for symbolic links, and as such there is no

    int dotIndex = fileName.lastIndexOf('.');
    return (dotIndex == -1) ? fileName : fileName.substring(0, dotIndex);
  }

  /**
   * Returns a {@link Traverser} instance for the file and directory tree. The returned traverser
   * starts from a {@link File} and will return all files and directories it encounters.
   *
   * <p><b>Warning:</b> {@code File} provides no support for symbolic links, and as such there is no

   */
  public static <N> ImmutableSet<N> reachableNodes(Graph<N> graph, N node) {
    checkArgument(graph.nodes().contains(node), NODE_NOT_IN_GRAPH, node);
    return ImmutableSet.copyOf(Traverser.forGraph(graph).breadthFirst(node));
  }

  // Graph mutation methods

  // Graph view methods

  /**
   * Returns a view of {@code graph} with the direction (if any) of every edge reversed. All other

   */
  public static <N> ImmutableSet<N> reachableNodes(Graph<N> graph, N node) {
    checkArgument(graph.nodes().contains(node), NODE_NOT_IN_GRAPH, node);
    return ImmutableSet.copyOf(Traverser.forGraph(graph).breadthFirst(node));
  }

  // Graph mutation methods

  // Graph view methods

  /**
   * Returns a view of {@code graph} with the direction (if any) of every edge reversed. All other