文件相关.

        File file = new File("E:\\A");
        File file1 = new File("E:\\B");
        String[] list = file.list();
        String[] list1 = file1.list();
        List<String> list2 = Arrays.asList(list);
        List<String> list3 = Arrays.asList(list1);
        List<String> list4 = new ArrayList<>(list2);
        List<String> list5 = new ArrayList<>(list3);
        System.out.println(list2);
        System.out.println(list3);
        list4.removeAll(list5);//用removeAll方法，必须是ArrayList<>。a.removeAll(b),求A中有B中没有的元素
        System.out.println(list4);

求两集合的交集

list5.retainAll(list4);
System.out.println(list5);