直接使用Arrays.asList()转数组，转变类型实际为AbstractList

1、直接将数组转换为list时List的类型为AbstractList

public static void main(String[] args) {
    String[] arr = {"A","B","C","D"};
    List<String> list1 = Arrays.asList(arr);
　　　//由数组转化来的list需使用ArrayList再次转换才可使用，否则只能以AbstractList使用
    List<String> list = new ArrayList<>(Arrays.asList(arr));
    System.out.println("list type:");
    System.out.println("list1是否是AbstractList类"+(list1 instanceof AbstractList));
    System.out.println("list1是否是AbstractList类"+(list1 instanceof ArrayList));
}

list type:
list1是否是AbstractList类true
list1是否是AbstractList类false