Java统计List重复元素方法

import java.util.*;

public class CountDuplicates {
    public static Map<String, Integer> countElements(List<String> list) {
        Map<String, Integer> countMap = new HashMap<>();
        for (String item : list) {
            countMap.put(item, countMap.getOrDefault(item, 0) + 1);
        }
        return countMap;
    }

    public static void main(String[] args) {
        List<String> items = Arrays.asList("apple", "banana", "apple", "orange", "banana", "apple");
        Map<String, Integer> result = countElements(items);
        System.out.println(result); // 输出: {orange=1, banana=2, apple=3}
    }
}

import java.util.*;
import java.util.stream.Collectors;

public class CountWithStream {
    public static Map<String, Long> countElementsWithStream(List<String> list) {
        return list.stream()
                   .collect(Collectors.groupingBy(e -> e, Collectors.counting()));
    }

    public static void main(String[] args) {
        List<String> items = Arrays.asList("apple", "banana", "apple", "orange", "banana", "apple");
        Map<String, Long> result = countElementsWithStream(items);
        System.out.println(result); // 输出: {orange=1, banana=2, apple=3}
    }
}

Map<String, Long> duplicates = list.stream()
    .collect(Collectors.groupingBy(e -> e, Collectors.counting()))
    .entrySet()
    .stream()
    .filter(entry -> entry.getValue() > 1)
    .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));