Помогите! Как работает?

result.put(word, result.get(word) + 1);

public class Solution {
    public static void main(String[] args) throws Exception {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

        ArrayList<String> words = new ArrayList<String>();
        for (int i = 0; i < 2; i++) {
            words.add(reader.readLine());
        }

        Map<String, Integer> map = countWords(words);

        for (Map.Entry<String, Integer> pair : map.entrySet()) {
            System.out.println(pair.getKey() + " " + pair.getValue());
        }
    }

    public static Map<String, Integer> countWords(ArrayList<String> list) {
        HashMap<String, Integer> result = new HashMap<String, Integer>();

        //напишите тут ваш код
        for (String word : list) {
            if (result.containsKey(word)) {
                result.put(word, result.get(word) + 1);
            } else {
                result.put(word, 1);
            }
        }
        return result;

    }

}