Is there a better way to write using the Java 8 to populate the LinkedHashMap?

Question

I have some code that splits a String of letters, make a List with that and later, populate a LinkedHashMap of Character and Integer with the letter and its frequency. The code is as following,

   List<String> values = Arrays.asList((subjects.split(",")));
            for (String value : values) {
                char v = value.charAt(0);
                map.put(v, map.containsKey(v) ? map.get(v) + 1 : 1);
            }
            map.put('X', 0);

How can I write it concisely with Java 8 ? Thanks.

Answer 1

Try this:

LinkedHashMap<Character, Long> counts = Pattern.compile(",")
        .splitAsStream(subjects)
        .collect(Collectors.groupingBy(
                s -> s.charAt(0),
                LinkedHashMap::new,
                Collectors.counting()));

If you must have an Integer count, you can wrap the counting collector like this:

Collectors.collectingAndThen(Collectors.counting(), Long::intValue)

Another option (thanks @Holger):

Collectors.summingInt(x -> 1)

As a side note, you could replace your looping update with this:

map.merge(v, 1, Integer::sum);