1.在平时的时候经常会用到求交集、补集、并集、差集的问题 本文通过引入org.apache.commons.collections4.CollectionUtils 进行很方便的解决

      ArrayList arrayList=new ArrayList();
      List<String> list = Arrays.asList("A", "A", "B", "C");
      List<String> list2 = Arrays.asList("E", "A", "F", "G");
      List<String> collate = CollectionUtils.collate(list, list2);
      System.out.println("两个集合合并"+collate);

      //通过集合求交集
      Collection<String> intersection = CollectionUtils.intersection(list, list2);
      System.out.println("交集is:"+intersection);

    // 通过从其他集合中减去一个集合的对象来获取新集合
      Collection<String> subtract = CollectionUtils.subtract(list, list2);
      System.out.println("集合相减is:"+subtract);

     //求并集
      Collection<String> union = CollectionUtils.union(list, list2);
      System.out.println("两个集合并集是:"+union);