String s = "aaaaabbbbbbooooollllltttmmmmm";
List<Character> characterList = input.chars()
                .mapToObj(c -> (char) c)
                .collect(Collectors.toList());

Map<Character, Long> mapCount = list.stream()
                .collect(Collectors.groupingBy(Character::charValue, Collectors.counting()));

int maxSum = Arrays.stream(arr)
                .reduce((sum, i) -> sum > 0 ? sum + i : i)
                .getAsInt();

Collections.max(map.entrySet(), Map.Entry.comparingByValue()).getValue();
Collections.max(map.entrySet(), Map.Entry.comparingByValue()).getKey();