Iterator and regular for loop

Question

I understand how iteration work but may be I need more knowledge about it. Can any one please show me the main difference between these two statements:

while (scanner.hasNext()) {
        tokenizer = new StringTokenizer(scanner.nextLine());
        numberOfItems = Integer.parseInt(tokenizer.nextToken());
        int[] numbers = new int[numberOfItems];
        for (int i:numbers) {
            numbers[i] = Integer.parseInt(tokenizer.nextToken());
        }
        System.out.println(isJolly(numbers));
    }

while (scanner.hasNext()) {
        tokenizer = new StringTokenizer(scanner.nextLine());
        numberOfItems = Integer.parseInt(tokenizer.nextToken());
        int[] numbers = new int[numberOfItems];
        for (int i = 0; i < numberOfItems; i++) {
            numbers[i] = Integer.parseInt(tokenizer.nextToken());
        }
        System.out.println(isJolly(numbers));
    }

why these giving me 2 different output?

Primitive arrays don't use an Iterator object. For arrays, the enhanced for loop is syntactic sugar. See Effective Java, Item 46. — Eric Cochran
– Eric Cochran, Commented Sep 30, 2015 at 0:09
so you are saying I ca not use Iterator with array?but I used before and it gave me correct output. — mlhazan
– mlhazan, Commented Sep 30, 2015 at 0:13
No, there literally is no Iterator. :) int[] nums can't spawn you an Iterator. You used the enhanced for loop. — Eric Cochran
– Eric Cochran, Commented Sep 30, 2015 at 0:16

ya_pulser · Accepted Answer · 2015-09-30 00:37:36Z

1

You have created empty array (array filled with zeroes).

    int[] numbers = new int[numberOfItems];

In case of

 for ( int i = 0; i < numbers.length; i++ ) ...

i starts from 0 and on each iteration it is incremented (i++). Iterations are finished when i became equals or more than numbers.length (aka numberOfItems). So sequence of i values is 0,1,2,3,4,5,...

In case of

for (int i:numbers) {

You iterate on each value taken from array and you will get sequence of zeroes ( 0,0,0,0,0, ...).

And yours number[i] = will update only the number[0] element of resulting array.

answered Sep 30, 2015 at 0:37

ya_pulser

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