Why is there (Integer) casting?

[hitesh_public]

Friends,

// Obtaining an array from an array list

import java.util.*;

class ArrayListToArray {

  public static void main(String[] args) {

    ArrayList al = new ArrayList();

    al.add(new Integer(1));
    al.add(new Integer(2));
    al.add(new Integer(5));
    al.add(new Integer(9));

    System.out.println("The contents of the array list are" + al);

    Object ia[] = al.toArray();

    int sum = 0;
    for(int i = 0; i < ia.length; i++) 
      sum += ((Integer)ia[i]).intValue();
      
    System.out.println("The sum is" + sum);
  }
}

What does this statement does?

sum += ((Integer)ia[i]).intValue();

Why is there (Integer) casting in the above code?

Thanks a lot.

[m00nchile]

Because non-generic Lists return objects. As you see, you declared the array to hold Object-type elements, so you need to cast them to Integer before you can use a mathematical operation on them. This is solved by using generics, instead of:

ArrayList list;

you use

ArrayList<Integer> list;

This way, the List will only accept Integer objects, and also return Integers (no need to cast).