How do you set the value from children list to parent list

Question

Inheritance in Java. Is it possible to do like this:

List<ParentEntity> loc = Locations,

where Locations is List<ChildEntity>

http://stackoverflow.com/questions/2745265/is-listdog-a-subclass-of-listanimal-why-arent-javas-generics-implicit — assylias, Nov 23 '12 at 15:51

Rohit Jain · Answer 1 · 2012-11-23T15:54:59.123

5

No you can't do that. Polymorphism is not allowed in generics.

However you can do: -

List<? extends ParentEntity> loc = new ArrayList<ChildEntity>();

Oh yes, you won't be able to add any new item to your list after that assignment, except null. That's a restriction you have to bear with.

So, you can first create your ArrayList<ChildEntity>, fill it, and then assign it to the LHS.

edited Nov 23 '12 at 15:54

answered Nov 23 '12 at 15:49

Rohit Jain

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And he wont be able to add anything else than `null` to his list – Jerome Nov 23 '12 at 15:50
Sorry, I had to reassign the answered mark to Jerome. His solution really helped me. I've just test it. Anyways thank you very much! – Sergey Nov 23 '12 at 16:18
@Sergey.. Ah! common. It's absolutely all right. You never have to feel sorry for changing your accepted answer. Accept the most suited answer, wihout 2nd thought. :) – Rohit Jain Nov 23 '12 at 16:19
Thank you! :) In any case this answer helped me as well – Sergey Nov 23 '12 at 17:02
@Downvoter.. Any particular reason for downvote that you think I deserve to know? – Rohit Jain Nov 23 '12 at 21:09

score 4 · Accepted Answer · answered Nov 23 '12 at 15:53

As @Rohit Jain said, his answer is limited.

You can have a workaround like this :

List<ParentEntity> loc = new ArrayList<ParentEntity>()
loc.addAll(locations);

This time, the limitation is that you lose the initial type of List implementation. And, more importantly, any modification to loc won't be seen on locations.

How do you set the value from children list to parent list

2 Answers2