Array of ArrayList

Question

import java.util.ArrayList;
import java.util.*;
import java.util.List;
class A
{
    public static void main(String args[])
    {
        ArrayList arrayOfArrayList[]=new ArrayList[2];
        int i;
        for(i=0;i<2;i++)
        {
            arrayOfArrayList[i] = new ArrayList<Integer>();
        }
        arrayOfArrayList[0].add(1);
        arrayOfArrayList[0].add(2);
        arrayOfArrayList[1].add(3);
        arrayOfArrayList[1].add(4);
        Integer arr[][] = new Integer[2][];
        arr[0] = arrayOfArrayList[0].toArray(arr[0]);
        arr[1] = arrayOfArrayList[1].toArray(arr[1]);
        for (Integer x : arr[0])
            System.out.print(x + " ");
    }
}

I am trying to create an array of arrayLists and later convert it to array. But the compile time error error: Incompatible type conversion object[] to Integer[]

Answer 1

Here you created raw type :

ArrayList arrayOfArrayList[]=new ArrayList[2];

If you need to store Integer there, you should use correct generics:

ArrayList<Integer> arrayOfArrayList[]=new ArrayList[2];