为什么我的HashMap内容不能打印？

Question

我正在编写一个逐行读入文本文件的程序 - 然后将每个句子存储在HashMap中，并将句子作为关键字，将该句子中的字母数作为对象。这是我写的代码，带有注释：

    FileReader reader = new FileReader(new File("src/test.txt"));
    BufferedReader br = new BufferedReader(reader);
    HashMap<String, Integer> map = new HashMap<String, Integer>();
    StringBuilder builder = new StringBuilder();
    String line, sentence;
    int letters = 0;
    try {
        // While there are more lines to read 
        while ((line = br.readLine()) != null) {
            String[] words = line.split(" "); // split line into words, add to array
            for (int i = 0; i < words.length; i++) { // loop through array
                letters += words[i].length(); 
                // if the word ends with "." then we have reached end of sentence
                if (Character.toString(words[i].charAt(words[i].length() - 1)) == ".") { 
                    for(String word : words) {
                        if(builder.length() > 0) {
                            builder.append(" ");
                        }
                        builder.append(word);
                    }
                    sentence = builder.toString(); // store sentence
                    map.put(sentence, letters); // add to HashMap
                    letters = 0; // restore letters back to 0
                }
            }
        }
    } catch (IOException e) {
        e.printStackTrace();
    }

    for(String key : map.keySet()) {
        System.out.println(key + " has " + map.get(key) + " letters");
    }

出于某种原因，最后在那个小的for循环中没有任何东西被打印出来。我注意到如果我在for循环之前写一个print语句来打印出我的HashMap的大小，它打印出“0” - 所以我假设我的HashMap没有被填充。

有谁知道为什么会这样？这是我正在使用的文本文件：

this is a test. 
this is a test. 
this is not a test. 
this is a test. 
this is not a test. 
not not not not not not not

非常感谢任何见解，欢呼。