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doubts in converting arraylists to array

sagar shiraguppi
Ranch Hand

Joined: Jul 16, 2007
Posts: 74
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
lowercase baba
Bartender

Joined: Oct 02, 2003
Posts: 11476
    
  16

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.


There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors
sagar shiraguppi
Ranch Hand

Joined: Jul 16, 2007
Posts: 74
Thank you Fred, you cleared my doubts
Wouter Oet
Saloon Keeper

Joined: Oct 25, 2008
Posts: 2700

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.

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.


"Any fool can write code that a computer can understand. Good programmers write code that humans can understand." --- Martin Fowler
Please correct my English.
 
It is sorta covered in the JavaRanch Style Guide.
 
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