Error: generic array creation with my own object

Question

I want to create a list that contains linked list of MyObject.

LinkedList<MyObject>[] list  = new LinkedList<MyObject>[n];

But it shows:

Main.java:19: error: generic array creation LinkedList<MyObject>[] list  = new LinkedList<MyObject>[n];

How can I create this kind of list?

Do you mean "a array of linked lists" or do you mean "a list or linked lists". For the second case see my answer (after all you asked for it), for the first case your code looks fine for older Java. — eckes
– eckes, Commented Oct 21, 2014 at 0:59
@afzalex The angle bracketed expressions (<...>) were hidden by the way posts are formatted. The editor did not add them, they appeared once the code was spaced in. — Radiodef
– Radiodef, Commented Oct 21, 2014 at 1:04
Oh! that is why I was thinking there is no problem here. But I am wondering how the answerers knew that, and started to answer. @Radiodef — afzalex
– afzalex, Commented Oct 21, 2014 at 1:07

Scary Wombat · Accepted Answer · 2014-10-21 01:09:44Z

1

Why are you trying to create an array of LinkedLists? it is after all already a List.

Change your code to

List <MyObject> list = new LinkedList<MyObject>();

if you want a collection of these LinkedLists then I suggest that you create a new List

List <LinkedList<MyObject>> theBigList = new ArrayList <> ();

and then you can add to this list

theBigList.add (list);

edited Oct 21, 2014 at 1:09

answered Oct 21, 2014 at 0:51

Scary Wombat

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5 Comments

Scary Wombat Over a year ago

@SleimanJneidi Thanks. If there is a good reason for a DV, I would really like to know about it so I can add value to this site.

afzalex Over a year ago

Before posting answer, have you checked that the problem is there? his code was working and not given any error for me. Now somebody has edited his question.

Sleiman Jneidi Over a year ago

Well, the question is edited now to a completely different question, maybe thats why, the DV was a better mind reader!

afzalex Over a year ago

Anyway, I removed my DV before getting too late. apologize. but I thought we should atleast first check if the OP was correct or not.

afzalex Over a year ago

Although I want to know if the last unedited code was working for you, with some other version of java, I tried 7 and 8.

3 revs · Accepted Answer · 2014-10-21 01:18:39Z

A List of Lists would look like:

List<List<MyObject>> listList = new LinkedList<>();
List<MyObject> list1 = new LinkedList<>();
List<MyObject> list2 = new LinkedList<>();
listList.add(list1);
listList.add(list2);
List<MyObject> list3 = listList.get(0);

And an Array of LinkedLists would look like:

@SuppressWarnings("unchecked")
List<MyObject>[] listArray = new LinkedList[n];
List<MyObject> list1 = new LinkedList<>();
List<MyObject> list2 = new LinkedList<>();
listArray[0] = list1;
listArray[1] = list2;
List<MyObject> list3 = listArray[0];

Both assume the diamond operator (<>) which is a Java 7 shortcut, but can be replaced with the full type (new LinkedList<MyObject> for the second and LinkedList<List<MyObject>> for the first case).

And the fact that arrays cannot be instantiated of generic type (due to all kinds of weird internals). See for example http://bugs.java.com/bugdatabase/view_bug.do?bug_id=5105887

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