我想您使用的源代码来自robertsedgewick和kevinwayn关于java算法实现的优秀书籍，第4版。
没有理由不让代码正常工作。请根据您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();
      }
    }
  }
}

如果使用指定的文本文件运行此程序，将生成类似以下内容的输出：

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

我介绍的主要变化是与计算 start 以及 goal 变量：

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

我假设您正在使用另一个文本文件，也许是另一个代码；如果提供了一个Assert，则Assert将失败或失败 StringIndexOutOfBounds 计算时将引发异常 goal 作为 substring 从索引 6 至 11 .
除此之外，算法应该可以正常工作。
也就是说，请注意，您正在构造一个超连通图，其中每个节点都有一个指向不同节点和自身的直接路径。也许这是你的目标，但要注意，当你做其他事情时，事情会变得有趣。
例如，如果不使用此代码：

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

你可以这样做：

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

算法的输出更有意义：

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

我想您使用的是java教科书中的代码
你的代码应该是

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;

public class words_sof {

    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));
            }
        }

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

            while (true) {
// ORIGINAL     String line = readTestFile.readLine();
// Should be
                String line = readValues.readLine();
                if (line == null) {
                    break;
                }

// ORIGINAL parse like this is not appropriate              
//              assert line.length() == 11;
//              String start = line.substring(0, 5);
//              String goal = line.substring(6, 11);
                // Use something like https://stackoverflow.com/questions/20728050/split-strings-in-java-by-words
                 String [] tokens = line.split("[\\s']");

                 String start = tokens[0];
                 String goal = tokens[1];

                BreadthFirstPaths bfs = new BreadthFirstPaths(g, words.indexOf(start));
                if (bfs.hasPathTo(words.indexOf(goal))) {
// Captions added for clarity                   
                    System.out.println("Distance : " + bfs.distTo(words.indexOf(goal)));
                    for (int v : bfs.pathTo(words.indexOf(goal))) {
                        System.out.print(" -> " + v);
                    }
                    System.out.println();
                } else
                    System.out.println("Nothing");
            }
        }
    }

}

请注意修改
//原始线条。
上面的代码产生

Distance : 1
 -> 0 -> 1
Distance : 1
 -> 0 -> 2
Distance : 1
 -> 3 -> 2