我想你正在使用Robert Sedgewick和Kevin Wayne的优秀著作中有关Java算法第四版中算法实现的源代码。

没有理由为什么你的代码不能正常工作。请根据你的代码考虑以下测试：

public static void main(String... args) throws IOException {
  ArrayList<String> words = new ArrayList<String>();
  words.add("hello");
  words.add("there");
  words.add("here");
  words.add("about");

  Graph g = new Graph(words.size());
  for(String word: words) {
    for(String word2: words){
      g.addEdge(words.indexOf(word), words.indexOf(word2));
    }
  }

  BufferedReader readValues = null;

  try {

    readValues =
        new BufferedReader(new InputStreamReader(new FileInputStream("values.txt")));

    String line = null;
    while ((line = readValues.readLine()) != null) {
      // assert line.length() == 11;
      String[] tokens = line.split(" ");
      String start = tokens[0];
      String goal = tokens[1];

      BreadthFirstPaths bfs = new BreadthFirstPaths(g, words.indexOf(start));
      if (bfs.hasPathTo(words.indexOf(goal))) {
        System.out.println("Shortest path distance from " + start + " to " + goal + " = " + bfs.distTo(words.indexOf(goal)));
        StringBuilder path = new StringBuilder();
        String sep = "";
        for (int v : bfs.pathTo(words.indexOf(goal))) {
          path.append(sep).append(v);
          sep = " -> ";
        }

        System.out.println("Shortest path = " + path.toString());
      } else System.out.println("Nothing");
    }

  } finally {
    if (readValues != null) {
      try {
        readValues.close();
      } catch (Throwable t) {
        t.printStackTrace();
      }
    }
  }
}

如果使用你指示的文本文件运行该程序，它将产生类似于以下内容的输出：

Shortest path distance from hello to there = 1
Shortest path = 0 -> 1
Shortest path distance from hello to here = 1
Shortest path = 0 -> 2
Shortest path distance from about to here = 1
Shortest path = 3 -> 2

我介绍的主要更改是与start和goal变量的计算有关的代码：

String[] tokens = line.split(" ");
String start = tokens[0];
String goal = tokens[1];

我假设你正在使用另一个文本文件，也许是另一个代码。与一个提供的断言将失败或StringIndexOutOfBounds当你计算将引发异常goal的substring从指数6到11。

除此之外，该算法应该可以正常工作。

话虽这么说，请注意，你正在构造一个图hyperconnected，其中每个节点都有一个指向不同节点及其本身的直接路径。也许这可能是你的目标，但请注意，当你执行其他操作时，事情会变得很有趣。

例如，如果使用以下代码代替：

for(String word: words) {
  for(String word2: words){
    g.addEdge(words.indexOf(word), words.indexOf(word2));
  }
}

你尝试这样的事情：

g.addEdge(words.indexOf("hello"), words.indexOf("there"));
g.addEdge(words.indexOf("hello"), words.indexOf("about"));
g.addEdge(words.indexOf("about"), words.indexOf("here"));

该算法的输出更具意义：

Shortest path distance from hello to there = 1
Shortest path = 0 -> 1
Shortest path distance from hello to here = 2
Shortest path = 0 -> 3 -> 2
Shortest path distance from about to here = 1
Shortest path = 3 -> 2