我非常喜欢 getOrElseUpdate 方法，在 mutableMap 中找到并在此处显示，首先是 Java，没有：
public static Map <String, Integer> wordCount (Scanner sc, String delimiters) {
Map <String, Integer> dict = new HashMap <String, Integer> ();
while (sc.hasNextLine ()) {
String[] words = sc.nextLine ().split (delimiters);
for (String word: words) {
if (dict.containsKey (word)) {
int count = dict.get (word);
dict.put (word, count + 1);
} else
dict.put (word, 1);
}
}
return dict;
}
是的 - WordCount，在 scala 中：
def wordCount (sc: Scanner, delimiter: String) = {
val dict = new scala.collection.mutable.HashMap [String, Int]()
while (sc.hasNextLine ()) {
val words = sc.nextLine.split (delimiter)
words.foreach (word =>
dict.update (word, dict.getOrElseUpdate (word, 0) + 1))
}
dict
}
它在 Java 8 中：
public static Map<String, Integer> wordCount(Scanner sc, String delimiters)
{
Map<String, Integer> dict = new HashMap<>();
while (sc.hasNextLine())
{
String[] words = sc.nextLine().split(delimiters);
Stream.of(words).forEach(word -> dict.merge(word, 1, Integer::sum));
}
return dict;
}
如果您想 100% 发挥功能：
import static java.util.function.Function.identity;
import static java.util.stream.Collectors.*;
public static Map<String, Long> wordCount(Scanner sc, String delimiters)
{
Stream<String> stream = stream(sc.useDelimiter(delimiters));
return stream.collect(groupingBy(identity(), counting()));
}
public static <T> Stream<T> stream(Iterator<T> iterator)
{
Spliterator<T> spliterator = Spliterators.spliteratorUnknownSize(iterator, 0);
return StreamSupport.stream(spliterator, false);
}
filter 和 sort 已经显示，但看看它们与地图的集成是多么容易：
def filterKeywords (sc: Scanner, keywords: List[String]) = {
val dict = wordCount (sc, "[^A-Za-z]")
dict.filter (e => keywords.contains (e._1)).toList . sort (_._2 < _._2)
}