Initialize List<List<Integer>> in Java

Use

List<List<Integer>> list = new ArrayList<List<Integer>>();

or since Java 1.7

List<List<Integer>> list = new ArrayList<>();

You can define it as List<List<Integer>> list = new ArrayList<List<Integer>>();.

Then while defining the inner List you can take care of initialising it as ArrayList<Integer>.

You can define it as List<List<Integer>> list = new LinkedList();

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