enhanced for-loop behavior for handling collection object

Question

As I am learner of Java.. I came across the following code

public static void main(String[] args) {
  ArrayList<String> a = new ArrayList<>();
  a.add("1");
  a.add("2");
  for(String str: a){
  a = new ArrayList<>();
  System.out.println(str);
  }
 }

I guessed the answer to be

1 null (since the reference is now pointing another object)

but the answer is

1 2

I am unable understand the behavior of enhanced for loop here.

Have you tried `System.out.println(a);` just after `System.out.println(str);`? What does it give you? You are essentially looping using a iterator in a for each. — Aniket Sahrawat, Mar 20 '18 at 12:10
Possible duplicate of [How does the Java 'for each' loop work?](https://stackoverflow.com/questions/85190/how-does-the-java-for-each-loop-work) — jrtapsell, Mar 20 '18 at 12:10
Yes , i tried that it is giving '[]' as output....what does '[]' indicates @AniketSahrawat — Namrata Shukla, Mar 20 '18 at 13:40

score 6 · Accepted Answer · answered Mar 20 '18 at 12:10

The enhanced for loop creates an Iterator to iterate of the elements of your ArrayList. Changing the a reference to refer to a new ArrayList doesn't affect the Iterator that was created by the loop.

Your loop is equivalent to

Iterator<String> iter = a.iterator();
while (iter.hasNext()) {
    String str = iter.next();
    a = new ArrayList<>();
    System.out.println(str);
}

Carcigenicate · Answer 2 · 2018-03-20T12:40:57.477

3

When you run

for(String str: a)

It gets an iterator from a, then iterates using that iterator. Reassigning a after it has the iterator will have no effect since it isn't using the a reference, it's using the iterator that a returned when the loop started.

edited Mar 20 '18 at 12:40

answered Mar 20 '18 at 12:11

Carcigenicate

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score 0 · Answer 3 · answered Mar 20 '18 at 12:17

0

This is because, enhanced for loop uses iterator. So changing the reference will not have any impact. You can check different scenarios here

answered Mar 20 '18 at 12:17

Vikas

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enhanced for-loop behavior for handling collection object

3 Answers3