CODEWITHSUNDEEP
javaarraylistcollections
adflixit
adflixit

Reputation: 39

How to access an element of collection inside the collection?

So I got this code:

List chunks = new ArrayList<ArrayList<Block>>(1);

And I need to get a child of an inner ArrayList.

Upvotes: 1

Views: 1148

Answers (2)

Suresh Atta
Suresh Atta

Reputation: 121998

First fix the declaration part 

List<List<Block>> chunks = new ArrayList<ArrayList<Block>>(1);

or even better if you are using Java 7

List<List<Block>> chunks = new ArrayList<>(1);

And then

chunks.get(0).get(0);

Will give you the inner element Block, assuming you have already added the elements in it.

If no elements added at that place, you'll run into exception.

Upvotes: 7

Eran
Eran

Reputation: 393841

List<List<Block>> chunks = new ArrayList<ArrayList<Block>>(1);

creates an empty ArrayList, so you can't get anything from it. Note that I changed the type of chunks. If you use a raw type (i.e. List), chunks.get() will return an instance of Object type, and you'll have to cast it (unsafely) to List<Block> in order to obtain elements from the inner List.

First you have to add something to it :

chunks.add (new ArrayList<Block>());

Then you can get the inner ArrayList and add an element to it :

chunks.get(0).add (new Block());

Then you can obtain the inner element via :

Block b = chunks.get(0).get(0);

Upvotes: 4

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