如何计算arrayList中相同值的出现次数

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;

public class ArrayListCount {
    public static void main(String[] args) {
        ArrayList<Integer> arrayList = new ArrayList<>();
        arrayList.add(1);
        arrayList.add(2);
        arrayList.add(3);
        arrayList.add(2);
        arrayList.add(1);
        arrayList.add(2);

        Map<Integer, Integer> countMap = new HashMap<>();
        for (Integer num : arrayList) {
            if (countMap.containsKey(num)) {
                countMap.put(num, countMap.get(num) + 1);
            } else {
                countMap.put(num, 1);
            }
        }

        for (Map.Entry<Integer, Integer> entry : countMap.entrySet()) {
            System.out.println("元素 " + entry.getKey() + " 出现次数：" + entry.getValue());
        }
    }
}