// Java code to demonstrate the concept of 
// array of ArrayList
  
import java.util.*;
public class Arraylist {
    public static void main(String[] args)
    {
        int n = 5;
  
        // Here al is an array of arraylist having
        // n number of rows.The number of columns on
        // each row depends on the user.
        // al[i].size() will give the size of the
        // i'th row
        ArrayList<Integer>[] al = new ArrayList[n];
  
        // initializing
        for (int i = 0; i < n; i++) {
            al[i] = new ArrayList<Integer>();
        }
  
        // We can add any number of columns to each
        // rows as per our wish
        al[0].add(1);
        al[0].add(2);
        al[1].add(5);
        al[2].add(10);
        al[2].add(20);
        al[2].add(30);
        al[3].add(56);
        al[4].add(34);
        al[4].add(67);
        al[4].add(89);
        al[4].add(12);
  
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < al[i].size(); j++) {
                System.out.print(al[i].get(j) + " ");
            }
            System.out.println();
        }
    }
}

1 2 
5 
10 20 30 
56 
34 67 89 12 

prog.java:15: warning: [unchecked] unchecked conversion
        ArrayList[] al = new ArrayList[n];
                                  ^
  required: ArrayList[]
  found:    ArrayList[]
1 warning

ArrayList<Integer>[] al = new ArrayList[n];