Using iterator interface or for each statement in Java

Question

Stack<String> sk = new Stack<String>();

sk.push("Hello");
sk.push("Hello1");
sk.push("Hello2");

There are two ways i am iterating this Stack Object.

for(String s : sk){
   System.out.println("The Values of String in SK" +sk);
}

// Way two..

Iterator<String> it=sk.iterator();
    while(it.hasNext())
    {
        String iValue=(String)it.next();
        System.out.println("Iterator value :"+iValue);
    }

What is the difference between these two?
Any Advantage if i choose one among them?
Which is the preferred way of iterating?

Arnout Engelen · Accepted Answer · 2011-09-07 10:19:08Z

4

The Iterator has the advantage that you can remove elements from the collection while iterating over it. Foreach may throw ConcurrentModificationExceptions there.

If you don't need that, I prefer the former way because it is easier to read.

answered Sep 7, 2011 at 10:19

Arnout Engelen

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1 Comment

aioobe Over a year ago

Why would he use a Stack if he needs to remove elements from the middle of the collection?

aioobe · Accepted Answer · 2011-09-07 10:20:31Z

1. What is the difference between these two?

Not much. The for-each loop construct actually relies on the iterator behind the curtains.

Further reading:

The For-Each Loop, official documentation / tutorial

2. Any Advantage if i choose one among them?

Mostly readability I would assume.

(If you need to access the iterator.remove() method, then obviously you would need to go with the explicit Iterator approach.) However, keep in mind that it's an optional operation and may not be supported by the underlying Stack implementation you're using.

Besides, the point of a Stack structure is that you don't remove elements in the middle.

3. Which is the preferred way of iterating?

Use the for-each approach, if that works for you.

oliholz · Accepted Answer · 2011-09-07 10:19:22Z

2

with the Iterator you can prevent a java.util.ConcurrentModificationException, when you modify the list while looping over them. Iterator.remove()

answered Sep 7, 2011 at 10:19

oliholz

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Comments

Jean Logeart · Accepted Answer · 2011-09-07 10:40:47Z

From Effective Java, by Joshua Bloch:

The for loop, in both its traditional and for-each forms, allows you to declare loop variables, limiting their scope to the exact region where they’re needed. (This region consists of the body of the loop as well as the initialization, test, and update preceding the body.)Therefore, prefer for loops to while loops, assuming the contents of the loop variable aren’t needed after the loop terminates.

To make it short:

the for-each loop is always type safe
the for-each loop is less prone to copy/paste errors (copy/paste iterator1 twice in your code!)
the for-each loop allows you to minimize the scope of local variables
the for-each loop is easier to read!

In summary, prefer for-each loops to while loops when you do not explicitly need a while loop.

asgs · Accepted Answer · 2011-09-07 10:19:58Z

1

Choosing between For each and an Iterator is just a matter of convenience. For each loop looks a bit cryptic especially to those who are used to the traditional for loop. The downside with Iterators, however, is that you've to cast the Object from the next() to the appropriate type, although your collection is not typed. With For each, everything is happening behind the scenes.

answered Sep 7, 2011 at 10:19

asgs

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1 Comment

Arnout Engelen Over a year ago

Actually, since java 1.5, Iterator is generic, so you don't need a cast if you added the appropriate generic parameters to your collection and iterator

Nivas · Accepted Answer · 2011-09-07 10:31:07Z

1

What is the difference between these two?

Nothing. Except for the extra code

Any Advantage if I choose one among them?

Yes. If you use the newer one (foreach), you have fewer lines and are therefore easier to read.

Which is the preferred way of iterating?

The foreach loop

You may want to read Nuances of the Java 5.0 for-each Loop and the official for-each loop tutorial

edited Sep 7, 2011 at 10:31

answered Sep 7, 2011 at 10:21

Nivas

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