converting an arraylist(integer) to an integer array

Question

I've tried couple of things to make this code work, but it didn't. my goal is to instantiate nums[] with numbers {0, 1, 2, .... n-1}. nums has no size, so I used list that instantiate nums with zeros. Keep in mind that the result must be an array (nums).

int nums[] = {}; int n = 0;
Scanner scanner = new Scanner(System.in);
System.out.println("Enter the number:");
n = scanner.nextInt();

ArrayList<Integer> listNum = new ArrayList<Integer>();
nums = new int[listNum.size()];//instantiate nums with zeros 
//nums = listNum.toArray(nums);
for (int i =0; i < n; i++){
    nums[i] = i;
}

Why not create nums after you ask the value for n ? The size will be known at that point. — Alexis C.
– Alexis C., Commented Oct 17, 2015 at 16:48

Gaël J · Accepted Answer · 2015-10-17 16:50:03Z

3

When you're writing this :

ArrayList<Integer> listNum = new ArrayList<Integer>();
nums = new int[listNum.size()];//instantiate nums with zeros

listnum has a size of 0, so nums won't be initialized as you want.

Why not just do :

nums = new int[n];

?

answered Oct 17, 2015 at 16:50

Gaël J

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1 Comment

Mohamed Ibrahim Over a year ago

thank you very much, but it means that I don't need to create arraylist . I just want to understand how it works.

Suresh Atta · Accepted Answer · 2015-10-17 16:51:01Z

3

Array's are fixed in size.

 nums = new int[listNum.size()];

That never works. You are initializing your array with zero elements. Once you declare the array size, you can't change that back.

What you are looking for is

    int nums[] = {}; int n = 0;
    Scanner scanner = new Scanner(System.in);
    System.out.println("Enter the number:");
    n = scanner.nextInt();
    nums = new int[n];//instantiate nums with entered size
    for (int i =0; i < n; i++){
        nums[i] = i;
    }

Just get rid of that ArrayList since you are know the size n

answered Oct 17, 2015 at 16:51

Suresh Atta

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Comments

Roman C · Accepted Answer · 2016-03-23 10:12:18Z

3

You don't need an ArrayList - if you take the input of n from the command line, you could just use it to initialize the array:

nums = new int[n];         
for (int i =0; i < n; i++){
    nums[i] = i;
}

edited Mar 23, 2016 at 10:12

Roman C

1

answered Oct 17, 2015 at 16:51

Mureinik

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