Java List集合去重的多种实现方法

/**
* 循环list中的所有元素然后删除重复
* @param list 待去重的list
* @return 去重后的list
*/
public static <T> List<T> removeDuplicate(List<T> list){
  for(int i=0;i<list.size()-1;i++){
      for(int j=list.size()-1;j>i;j--){
          if (list.get(j).equals(list.get(i))){
              list.remove(j);
          }
      }
  }
  return list;
}

/**
 * 通过HashSet去重
 * @param list 待去重的list
 * @return 去重后的list
 */
public static <T> List<T> removeDuplicateHashSet(List<T> list){
    HashSet<T> hs = new HashSet<>(list);
    list.clear();
    list.addAll(hs);
    return list;
}

/**
 * 删除List中重复元素，并保持顺序
 * @param list 待去重的list
 * @return 去重后的list
 */
public static <T> List<T> removeDuplicateKeepOrder(List<T> list){
    Set set = new HashSet();
    List<T> newList = new ArrayList<>();
    for (T element : list) {
        //set能添加进去就代表不是重复的元素
        if (set.add(element)) newList.add(element);
    }
    list.clear();
    list.addAll(newList);
    return list;
}

/**
 * 利用list.contain() 去重
 * @param list
 * @return
 */
public static <T> List<T> removeDuplicateContain(List<T> list){
    List<T> listTemp = new ArrayList<>();
    for (T aList : list) {
        if (!listTemp.contains(aList)) {
            listTemp.add(aList);
        }
    }
    return listTemp;
}

List filterList = list.stream().filter(user -> user.getAge() >= 40)        .collect(toList());

JSONObject jsonObject = JSONObject.parseObject(forEntity.getBody());
        String content = jsonObject.getString("content");
        JSONArray jsonArray = JSONObject.parseArray(content);
        for (int i = jsonArray.size() - 1; i >= 0; i--) {
            JSONObject jsonObject1 = jsonArray.getJSONObject(i);
            String caseId = jsonObject1.getString("caseId");
            QueryWrapper queryWrapper=new QueryWrapper();
            queryWrapper.eq("user_id",caseInfoQueryParam.getUserId());
            queryWrapper.eq("case_id",caseId);
            queryWrapper.last("limit 1");
            CaseInfo caseInfo = caseInfoMapper.selectOne(queryWrapper);
            logger.info("案件绑定详情去重的案件->{}",caseInfo);
            if (caseInfo!=null){
                jsonArray.remove(i);
            }
        }

classEntities.stream().collect(Collectors.groupingBy(ClassEntity::getGrade));

List<ClassEntity> distinctClass = classEntities.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(o -> o.getProfessionId() + ";" + o.getGrade()))), ArrayList::new));

List<String> classNameList = new ArrayList(new HashSet(classNames));

    public static void main(String[] args) {
        ArrayList<String> arrayList = new ArrayList();
        arrayList.add("111");
        arrayList.add("222");
//        arrayList.stream().forEach(s -> {
//            arrayList.remove(s);
//                    System.out.println(arrayList.size());
//                }
//        );
        for (int i = 0; i < arrayList.size(); i++) {
            arrayList.remove(i);
            i--;
        }
        System.out.println(arrayList);
    }