How does a for each loop guard against an empty list?

Question

I read on http://www.leepoint.net/notes-java/flow/loops/foreach.html. the for each equivalent to

for (int i = 0; i < arr.length; i++) { 
     type var = arr[i];
      body-of-loop
}

is

for (type var : arr) {
      body-of-loop
}

My question is how does a for each loop work for an empty list. I know for the regular for loop, the arr.length will just evaluate to 0 and the loop wont execute. What about the for each loop?

Solution 1

My question is how does a for each loop work for an empty list

ForEach also works in the same way. If the length is zero then loop is never executed.

The only difference between them is use ForEach loop when you want to iterate all the items of the list or array whereas in case of normal for loop you can control start and end index.

Solution 2

It uses the iterator of the Iterable collection, e.g. List. It is the duty of the implementer of the Iterator to write the hasnext() method to return false if there is no next item which will be the case if the collection is empty

Solution 3

Yes, it is equivalent.

If the list is empty, the for-each cycle is not executed even once.

Comments

[Eran]

But the question is about an array, not a Collection.

[ChiefTwoPencils]

You can always control the end of the for-each loop with if(something) break; IOW, you don't have to iterate the entire contents.

[Eran]

How does it answer the question? The OP knows the two code samples in the question are equivalent, and asks how the foreach loop works for an empty array, not whether it works.

[libik]

@Eran - Second sentence is answering the question, for empty list it is not executed (it means, it works and it is not executed, you cant say more about it).

[committedandroider]

I like this one but can you clarify on java docs, it says that an iterator iterates over a collection?

[user3810043]

It is in the language specification section 14.14.2 In brief, if the collection (small c) is an array then the compiler converts the code to a standard for loop with an int counter and if the collection (small c) is an Iterable (which includes the Collection classes) then it calls the iterator.