Java for each loop working

Question

I was working on certain task, when incidentally did something wrong according to me but the code executed and provided correct result. I was little surpris

Answer 1

It is of course not a problem to add something to a completely different list than the one you are currently traversing, as you did with the line mylist = new ArrayList(); Even though the variable still has the same name, it will point to an entirely different list.

The reason why you cannot add something to a list that is currently being "walked through" is, that the internal implementation of that list might not be able to ensure, that you still get the same order of elements and especially not all remaining elements as you would expect. This can be understand best if you imagine that you are using a sorted list: you put in a new element, but whether or not you see that element is undefined, as it depends on where you are and what you insert. As Java doesn't know if you are ok with that, it takes the safe road and throws an Exception.

There are however lists that are well capable of being able to be modified during traversal, mostly the concurrent lists in the concurrent package.