Java 8 Stream用于确定文本文件中的最大计数

Question

对于我的任务,我必须用循环来替换for循环,这些循环计算文本文档中单词的频率,并且我无法计算出TODO部分.

String filename = "SophieSallyJack.txt";
if (args.length == 1) {
    filename = args[0];
}
Map<String, Integer> wordFrequency = new TreeMap<>();

List<String> incoming = Utilities.readAFile(filename);

wordFrequency = incoming.stream()
    .map(String::toLowerCase)
    .filter(word -> !word.trim().isEmpty())
    .collect(Collectors.toMap(word -> word, word -> 1, (a, b) -> a + b, TreeMap::new));                

int maxCnt = 0;

// TODO add a single statement that uses streams to determine maxCnt
for (String word : incoming) {
    Integer cnt = wordFrequency.get(word);
    if (cnt != null) {
        if (cnt > maxCnt) {
            maxCnt = cnt;
        }
    }
}
System.out.print("Words that appear " + maxCnt + " times:");

我试过这个:

wordFrequency = incoming.parallelStream().
    collect(Collectors.toConcurrentMap(w -> w, w -> 1, Integer::sum));

但这不对,我不确定如何将maxCnt合并到流中.

Answer 1

假设您从文件中提取了所有单词，List<String>可以使用这种方法计算每个单词的单词计数，

Map<String, Long> wordToCountMap = words.stream()
                .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));

然后可以使用上面的方法计算最常用的单词，map如下所示，

Entry<String, Long> mostFreequentWord = wordToCountMap.entrySet().stream()
    .max(Map.Entry.comparingByValue())
    .orElse(new AbstractMap.SimpleEntry<>("Invalid", 0l));

如果您愿意，您可以将上述两个管道一起更改，

Entry<String, Long> mostFreequentWord = words.stream()
    .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()))
    .entrySet().stream()
    .max(Map.Entry.comparingByValue())
    .orElse(new AbstractMap.SimpleEntry<>("Invalid", 0l));

更新

Optional根据以下讨论，从计算中返回 an 总是好的，如下所示，

Optional<Entry<String, Long>> mostFreequentWord = words.stream()
    .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()))
    .entrySet().stream()
    .max(Map.Entry.comparingByValue());