/**
    * 方法1，求兩個(gè)集合的交集
    *
    * @param arr1
    * @param arr2
    * @return
    */
   public List<Object> intersectionForList_1(List<Object> arr1, List<Object> arr2) {
       long startTime = System.currentTimeMillis();
       List<Object> result = new ArrayList<>();
       for (Object arr : arr1) {
           if (arr2.contains(arr)) {
               result.add(arr);
           }
       }
       long endTime = System.currentTimeMillis();
       log.info("intersectionForList_1：" + (endTime - startTime));
       return result;
   }

 
  /**
   * 方法2，求兩個(gè)集合交集，（迭代器）
   *
   * @param arr1
   * @param arr2
   * @return
   */
  public List<Object> intersectionForList_2(List<Object> arr1, List<Object> arr2) {
      long startTime = System.currentTimeMillis();
      List<Object> resultList = new ArrayList<>();
      List<Object> maxList;
      List<Object> minList;
      if (arr1.size()>arr2.size()){
          maxList = arr1;
          minList = arr2;
      }else {
          maxList = arr2;
          minList = arr1;
      }
      Iterator<Object> iterator = maxList.iterator();
      while (iterator.hasNext()){
          Object next = iterator.next();
          if (minList.contains(next)){
              resultList.add(next);
          }
      }
      long endTime = System.currentTimeMillis();
      log.info("intersectionForList_2：" + (endTime - startTime));
      return resultList;
  }

    /**
     * 方法3，求兩個(gè)集合交集，（map）
     *
     * @param arr1
     * @param arr2
     * @return
     */
    public List<Object> intersectionForList_3(List<Object> arr1, List<Object> arr2) {
        long startTime = System.currentTimeMillis();
        List<Object> resultList = new ArrayList<>();
        Map<String,Object> map = new HashMap<>();
        arr1.forEach(a1->{
            map.put(a1+"",a1);
        });
        arr2.forEach(a2->{
            Object obj = map.get(a2 + "");
            if (obj!=null){
                resultList.add(obj);
            }
        });
        long endTime = System.currentTimeMillis();
        log.info("intersectionForList_3：" + (endTime-startTime));
        return resultList;
    }

    /**
     * 方法4，求兩個(gè)集合交集，（forEasy）
     * @param arr1
     * @param arr2
     * @return
     */
    public List<Object> intersectionForList_4(List<Object> arr1, List<Object> arr2){
        long startTime = System.currentTimeMillis();
        List<Object> resultList = new ArrayList<>();
        arr1.stream().forEach(a1->{
            if (arr2.contains(a1)){
                resultList.add(a1);
            }
        });
        long endTime = System.currentTimeMillis();
        log.info("intersectionForList_4：" + (endTime-startTime));
        return resultList;
    }