Java for each loop

I'm working on a task when I accidentally make a mistake, but the code executes and provides the correct result I was a little surprised and remembered how all this worked for each loop

public static void main( String[] args )
{
    String myInput = "hello,hi,how are you ";
    String[] splitted = myInput.split(",");
    List<String> mylist = new ArrayList<String>();
    for (String output : splitted) 
    {
        mylist.add(output);
    }


    for (String output : mylist) 
    {
        System.out.println(output);
        mylist = new ArrayList<String>(); //It worked 
        mylist.add(output);
    }

    for (String output : splitted) 
    {
        mylist.add(output);
    }

    for (String output : mylist) 
    {
        System.out.println(output);             
        mylist.add(output); // After this line it threw exception java.util.ConcurrentModificationException
    }

}

I'd like to know that during the search, I found another article saying that if we use the iterator method, we can delete elements from the list, so I tried,

for (String output : splitted) 
{
    mylist.add(output);
}
for (Iterator iterator2 = mylist.iterator(); iterator2.hasNext();)
{
    String string = (String) iterator2.next();
    System.out.println(string);
    iterator2.remove(); //It worked but if I used the same thing to remove element from original list it threw exception.
}

Now I just want to know what happens behind each loop referenced above I want to know the technical aspect. I know I can't modify the set of each loop, but in some cases, how does it work?

Solution

1. for (String output : splitted) 
    {
        mylist.add(output);
    }

This adds each output string in the split array to the mylist list

2. for (String output : mylist) 
{
      System.out.println(output);
      mylist = new ArrayList<String>(); //It worked 
      mylist.add(output);
}

The for statement is managed by the following products:

for ( FormalParameter : Expression )
            Statement

Where expression must be Java Lang. Iterable or an instance of an array So each cycle is equivalent to:

Iterator<String> iterator = mylist.iterator();
while (iterator.hasNext()) {
    System.out.println(output);
    mylist = new ArrayList<String>(); //It worked 
    mylist.add(output);
}

Here is mylist Iterator () will return a new instance of iterator type:

public Iterator<E> iterator() {
        return new Itr();
}

Therefore, even if you are creating new ArrayList instances and assigning them to mylist at each iteration, the iterator obtained from the original mylist will still have a reference to the original mylist and will continue to iterate over the elements of the original mylist An iterator maintains a reference to the list it creates The assignment mylist = new ArrayList < string > () has no effect on the data processed by the iterator because it changes the variable mylist rather than the list itself

3. for (String output : mylist) 
    {
        System.out.println(output);             
        mylist.add(output); // After this line it threw exception java.util.ConcurrentModificationException
    }

The following statement explains this behavior It is copied from ArrayList doc:

4. for (Iterator iterator2 = mylist.iterator(); iterator2.hasNext();)
{
    String string = (String) iterator2.next();
    System.out.println(string);
    iterator2.remove(); //It worked but if I used the same thing to remove element from original list it threw exception.
}

The above statement also explains the behavior of the for loop: when iterating through the list, the iterator's own remove or add methods can modify the list structurally