ArrayList中元素的频率

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

public class FrequencyCalculator {
    public static void main(String[] args) {
        ArrayList<Integer> arrayList = new ArrayList<>();
        // 添加元素到ArrayList
        arrayList.add(1);
        arrayList.add(2);
        arrayList.add(1);
        arrayList.add(3);
        arrayList.add(2);

        // 计算元素频率
        HashMap<Integer, Integer> frequencyMap = new HashMap<>();
        for (Integer element : arrayList) {
            if (frequencyMap.containsKey(element)) {
                frequencyMap.put(element, frequencyMap.get(element) + 1);
            } else {
                frequencyMap.put(element, 1);
            }
        }

        // 打印结果
        for (Map.Entry<Integer, Integer> entry : frequencyMap.entrySet()) {
            System.out.println("元素 " + entry.getKey() + " 的频率为 " + entry.getValue());
        }
    }
}