Array of Arraylists in Java

Arrays of parameterized types are not allowed i.e.

ArrayList<Integer>[] group = new ArrayList<Integer>()[4]

Arrays of a ArrayList or any Java collection can be done as below

ArrayList<ArrayList<Integer>> group = new ArrayList<ArrayList<Integer>>(4);

Another way is if REALLY need array (bad design!):

ArrayList[] group = new ArrayList[4];
ArrayList group[] = new ArrayList[4];
ArrayList<Integer>[] group = new ArrayList[4];
ArrayList<Integer>[] group = (ArrayList<Integer>[])new ArrayList[4];

Code snippet of Array of Arraylist

ArrayList<ArrayList<Integer>> array = 
    new ArrayList<ArrayList<Integer>>(5);

for(int i =0; i < 5; i++) {

  ArrayList<Integer> s = new ArrayList<Integer>();

  for (int j=0; j < 5; j++) {
    s.add(j);
  }

  array.add(s);
}