获取list集合中重复的元素

方法1

   List<String> words = Arrays.asList("a", "b", "c", "d", "a", "d");
        List<String> results = HashMultiset.create(words).entrySet().stream()
                .filter(w -> w.getCount() > 1)
                .map(Multiset.Entry::getElement)
                .collect(Collectors.toList());
        System.out.println(results);

方法2

可以修改返回值 返回去重的集合

  public static <E> List<E> getListDuplicateElements(List<E> list){
        List<E> words = list;
        Set<E> repeated = new HashSet<>();
        List<E> results = new ArrayList<>();
        for (E word : words) {
            if (!repeated.add(word)) {
                results.add(word);
            }
        }
       return  results;
    }

方法3

导入guava依赖

        <!-- https://mvnrepository.com/artifact/com.google.guava/guava -->
        <dependency>
            <groupId>com.google.guava</groupId>
            <artifactId>guava</artifactId>
            <version>31.0-jre</version>
        </dependency>

List<String> words = Arrays.asList("a", "b", "c", "d", "a", "d");
List<String> results = new ArrayList<>();
for (Multiset.Entry<String> entry : HashMultiset.create(words).entrySet()) {
  if (entry.getCount() > 1) {
    results.add(entry.getElement());
  }
}
System.out.println(results);

　　Lambda 来使用guava

List<String> words = Arrays.asList("a", "b", "c", "d", "a", "d");
List<String> results = HashMultiset.create(words).entrySet().stream()
    .filter(w -> w.getCount() > 1)
    .map(Multiset.Entry::getElement)
    .collect(Collectors.toList());
System.out.println(results);　　

方法4

 public List getRepeatList(List list) {
        List list2 = new ArrayList();
        for (int i = 0; i < list.size(); i++) {
            for (int j = i + 1; j < list.size(); j++) {
                if (list.get(i) !="" && list.get(i).equals(list.get(j))) {
                    list2.add(list.get(i));
                    break;
                }
            }
        }
        return list2;
    }

　　

    /**
     * 获取list 集合重复元素
     *
     * @param list
     * @param <E>
     * @return
     */
    public static <E> List<E> getDuplicateElements(List<E> list) {
        return list.stream() .filter( i -> i!="")                           // list 对应的 Stream 并过滤""
                .collect(Collectors.toMap(e -> e, e -> 1, Integer::sum)) // 获得元素出现频率的 Map，键为元素，值为元素出现的次数
                .entrySet()
                .stream()                       // 所有 entry 对应的 Stream
                .filter(e -> e.getValue() > 1)         // 过滤出元素出现次数大于 1 (重复元素）的 entry
                .map(Map.Entry::getKey)                // 获得 entry 的键（重复元素）对应的 Stream
                .collect(Collectors.toList());         // 转化为 List
    }

　　转自：(3条消息) 获取list集合中重复的元素_妃宫千早的博客-CSDN博客_list获取重复数据