Java a集合合并B集合 java集合取并集

/**
      * @Description: 取交集
      * @Param: [list1, list2]
      * @Return: java.util.List<java.lang.String>
      * @Author: 
      * @Date: 2022/6/28 15:35
      **/
     public List<String> getAndRes(List<String> list1, List<String> list2) {
         if (null != list1 && list1.size() != 0) {
             if (null == list2 || list2.size() == 0) {
                 return list1;
             } else {
                 return list1.stream().filter(list2::contains).collect(Collectors.toList());
             }
         } else {
             return list2;
         }
     }
 

     /**
      * @Description: 取并集
      * @Param: [list1, list2]
      * @Return: java.util.List<java.lang.String>
      * @Author: 
      * @Date: 2022/6/28 15:35
      **/
     public List<String> getORRes(List<String> list1, List<String> list2) {
         list1.addAll(list2);
         return list1.stream().distinct().collect(Collectors.toList());
     }