2d arraylist in java

1int vertexCount = 3;
2ArrayList<ArrayList<Integer>> graph = new ArrayList<>(vertexCount);
3//Next, we'll initialize each element of ArrayList with another ArrayList:
4
5for(int i=0; i < vertexCount; i++) {
6    graph.add(new ArrayList());
7}

1List<List<String>> listOfLists = new ArrayList<List<String>>(size); 
2for(int i=0; i<size; i++) {
3	listOfLists.add(new ArrayList<String>());
4}

1ArrayList<ArrayList<Object>> a = new ArrayList<ArrayList<Object>>();