what classes do you need for an array arraylist in java code example

Example: arraylist of arraylist

public static void main(String[] args) {
    ArrayList> outer = new ArrayList>();
    ArrayList inner = new ArrayList();        

    inner.add(100);     
    inner.add(200);
    outer.add(inner); // add first list
    inner = new ArrayList(inner); // create a new inner list that has the same content as  
                                           // the original inner list
    outer.add(inner); // add second list

    outer.get(0).add(300); // changes only the first inner list

    System.out.println(outer);
}