Item 优先选择流中没有副作用的函数

map<string, long> freq = new hashmap<>();
try (stream<string> words = new scanner(file).tokens()) {
    words.foreach(word -> {
        freq.merge(word.tolowercase(), 1l, long::sum);
    });
}

map<string, long> freq;
try (stream<string> words = new scanner(file).tokens()) {
    freq = words.collect(collectors.groupingby(string::tolowercase, collectors.counting()));
}

list<string> topten = freq.entryset().stream()
    .sorted(map.entry.<string, long>comparingbyvalue().reversed())
    .limit(10)
    .map(map.entry::getkey)
    .collect(collectors.tolist());

map<string, long> freq;
try (stream<string> words = new scanner(file).tokens()) {
    freq = words.collect(collectors.tomap(
        string::tolowercase, 
        word -> 1l, 
        long::sum
    ));
}

map<artist, album> topalbums = albums.stream()
    .collect(collectors.tomap(
        album::getartist,
        function.identity(),
        binaryoperator.maxby(comparator.comparing(album::sales))
    ));

String result = Stream.of("came", "saw", "conquered")
    .collect(Collectors.joining(", ", "[", "]"));