Why this code gives error

Question

Here Teacher is parent of Student

List<Student> list = new ArrayList<>();
List<Teacher> list1 = list;

// But this code works like a charm
List<Student> list = new ArrayList<>();
List<Teacher> list1 = new ArrayList<>();
list1.addAll(list);

Please explain it to me.
Please do not provide any link

Answer 1

Thanks but this is not what i want

Answer 2

I am just trying to know why this code gives error

Answer 3

I doubt if we can directly refer it like that without actually creating an instance of it. You can try this and let me know if it worked or not. Just an opinion.

List<Teacher> list1 = new ArrayList<>(list);
OR
List<Teacher> list1 = new ArrayList<>();
list1 = list;

Answer 4

If you can share a little bit more on what actually you are trying to achieve then probably it would be helpful for others to answer.

Answer 5

I think its giving an error because you havent specified the type of list whether its an integer or string

Answer 6

Hello Sumit Programmer😎😎

Upcasting treats your list as List but the object is still an ArrayList.

You can not just convert a List into an ArrayList.
I am not completely sure but:

List<Student> list = new ArrayList<>()

-> upcast works automatically

But in here you need to cast manually:

List<Teach> list1 = (ArrayList) list;