Why is there (Integer) casting?

Friends,

Code:

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// 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);
  }
}

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What does this statement does?

Code:

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

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

Thanks a lot.

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:

Code:

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ArrayList list;

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you use

Code:

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ArrayList<Integer> list;

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