doubts in converting arraylists to array

[sagar shiraguppi]

hi guys, I am converting arraylist into array..
Please let me know what exactly is happening in the line which is in italic and bold. Other lines of code I understood, please anyone explain me what exactly that particular line of code is doing..
code is as follows


ArrayList arl = new ArrayList();

// Add elements to the array list
arl.add(new Integer(1));
arl.add(new Integer(2));
arl.add(new Integer(3));
arl.add(new Integer(4));

System.out.println("Contents of al: " + arl);

// get array
Object ia[] = arl.toArray();
int sum = 0;

// sum the array
for (int i = 0; i < ia.length; i++) {
sum += ((Integer) ia[i]).intValue();
}

[fred rosenberger]

ia is an array of objects.

ia[i] gets you the i'th element in that array.

(Integer) ia[i]) casts that object reference to an Integer.

((Integer) ia[i]).intValue() gets you the int value of the Integer.

sum += ((Integer) ia[i]).intValue(); adds the int value to whatever is currently in sum.

[sagar shiraguppi]

Thank you Fred, you cleared my doubts

[Wouter Oet]

You don't even need the array use can just use to ArrayList to iterate through it. And if you use a generic ArrayList then it's even easier.

public static void main(String... args) {
	List<Integer> list = new ArrayList<Integer>(); 
	addValuesToList(list);
	System.out.println(sum(list));
}

public static void addValuesToList(List<Integer> list) {
	list.add(1); 
	list.add(2); 
	list.add(3); 
	list.add(4); 
}

public static int sum(List<Integer> list) {
	int sum = 0;
	for(int i: list)
		sum += i;
		
	return sum;
}
   

If you do need the array for omitted reasons then use: Integer[] array = list.toArray(new Integer[list.size()]); Because then you don't need to cast.